What you need to know before getting vaccinated
The FDA has authorized three COVID-19 vaccines (use of the Johnson & Johnson vaccine has been temporarily suspended). As more people get their shots, we will learn how long protection lasts. And we will gain answers to important questions, including whether vaccinations reduce the risk of infecting others. Though we cannot yet let up on masking and physical distancing, the vaccines offer hope that an end to this pandemic is in sight.
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Which vaccines has the FDA authorized for COVID-19?
On December 11, 2020, the FDA granted emergency use authorization (EUA) to an mRNA COVID-19 vaccine developed by Pfizer and BioNTech. One week later, the FDA granted EUA to an mRNA COVID-19 vaccine developed by Moderna. On April 13, 2021, the FDA and CDC recommended pausing use of the Johnson & Johnson vaccine while they investigate reports of an extremely rare but severe type of blood clot occurring after vaccination. The Johnson & Johnson vaccine had been granted EUA by the FDA in late February 2021.
How long will protection from the COVID-19 vaccines last?
Both the Pfizer/BioNTech and Moderna mRNA vaccines protect against COVID-19 for at least six months. This represents the minimum period of protection; only with time will we learn how much longer protection lasts. (The Johnson & Johnson vaccine has not been available long enough to collect six months of data.)
In a press release, Pfizer/BioNTech announced that their vaccine has been 91.3% effective in preventing COVID-19 up to six months after the second dose of the two-dose regimen. It was also found to be 95.3% to 100% effective at preventing severe disease (the number varied slightly depending on which definition of "severe disease" was used in the analysis). These results came from an interim analysis of Pfizer/BioNTech's Phase 3 clinical trial.
The Moderna vaccine results, published in NEJM, found that antibodies created by the body in response to the vaccine continued to exist at high levels six months after the second dose of the two-dose regimen.
Why did the FDA and CDC recommend pausing use of the Johnson & Johnson COVID-19 vaccine?
On April 13, 2021, the FDA and CDC jointly recommended pausing use of the Johnson & Johnson COVID-19 vaccine until the agencies can review the cases of a rare but serious type of blood clot that were reported in six women who received the Johnson & Johnson vaccine. The CDC's Advisory Committee on Immunization Practices (ACIP) and the FDA will meet this week to review the evidence.
Since the FDA granted emergency use authorization (EUA) for the Johnson & Johnson vaccine in late February, more than 6.8 million doses of the one-dose vaccine have been given. The six reported blood clot cases all occurred in women between the ages of 18 and 48, between six and 13 days after vaccination. All experienced a type of blood clot called cerebral venous sinus thrombosis, together with low levels of blood platelets (called thrombocytopenia).
While calling the risk of experiencing a blood clot after vaccination "extremely rare," the FDA and CDC are advising anyone who experiences the following symptoms within three weeks of receiving the Johnson & Johnson vaccine to contact their doctor:
- severe headache
- abdominal pain
- leg pain
- shortness of breath.
The clotting issue reported with the Johnson & Johnson vaccine is similar to the rare cases of unusual blood clots that the European Medicines Agency linked to the AstraZeneca vaccine.
I recently got the Johnson & Johnson COVID-19 vaccine. Am I at risk for a blood clot?
More than 6.8 million doses of the Johnson & Johnson COVID-19 vaccine have been given in the US since it received emergency use authorization from the FDA in late February 2021. Through April 12th, there have been six reported cases of a serious blood clotting issue. The FDA and CDC have called the risk of experiencing a blood clot after vaccination "extremely rare."
The six reported blood clot cases all occurred in women between the ages of 18 and 48, between six and 13 days after vaccination. All experienced a type of blood clot called cerebral venous sinus thrombosis, together with low levels of blood platelets (called thrombocytopenia).
Contact your doctor if you experience any of the following symptoms within three weeks of receiving the Johnson & Johnson vaccine:
- severe headache
- abdominal pain
- leg pain
- shortness of breath.
How have the vaccines performed in the real world? Are they working as well as they did in clinical trials?
In a study published online in MMWR, the CDC reported that people who had received both doses of either mRNA vaccine (Pfizer/BioNTech or Moderna) were 90% less likely to get infected with COVID-19 than people who were not vaccinated. In clinical trials, the vaccines were 95% (Pfizer/BioNTech) and 94.1% (Moderna) effective.
The MMWR study enrolled 3,950 adults who were at high risk of exposure to the virus due to their jobs, and followed them for 13 weeks beginning in mid-December 2020. About 63% of the study participants received both doses of vaccine during the study period and an additional 12% received one dose during the study. Each week, the study participants sent a nasal swab for PCR testing, and they reported any symptoms, allowing the researchers to identify both symptomatic and asymptomatic infections.
A total of 180 COVID-19 infections occurred during the study period. Of these, 161 infections were in people who were unvaccinated, compared to three infections in people who were fully vaccinated. Sixteen people who had received only their first vaccine dose at least two weeks earlier were infected. While this translates to one dose preventing 80% of infections, the study did not measure how well the vaccine protects people who do not get the second dose.
The researchers did not comment on variants, and the study was not designed to measure the effectiveness of the vaccines against them. However, it's worth noting that several viral variants were circulating during the study period.
Why are some people hesitant about getting a COVID vaccine?
It's natural to want to make an informed decision about the COVID-19 vaccine. Fortunately, the safety of the vaccine seen in the clinical trials has been verified by the real-world results.
Warp speed? Yes, the speed with which the COVID-19 vaccines were developed was incredibly fast. But the science and technology to make it happen came after decades of research.
COVID-19 mRNA vaccines are new, but scientists have been studying mRNA for many years. They cannot change your DNA. The mRNA sends a message to the body's cells to make only a specific protein, not a virus, that stimulates the immune system to give you protection. Experts predict that most vaccines in the future will use mRNA technology.
If you still have doubts about the vaccine, we recommend this short video produced by the Black Women's Health Imperative.
Some communities, particularly communities of color, may have historical reasons to doubt the health care system. But these communities have also been among the hardest hit by this pandemic, and like all of us, have a lot to gain from vaccination.
The Black Women's Health Imperative is a national organization dedicated to improving the health and wellness of Black women and girls.
I'm vaccinated. What can I do now?
Starting two weeks after your final COVID-19 vaccine dose, you can start enjoying some additional freedoms, while continuing to take precautions like mask wearing, physical distancing, and avoiding large groups. That's according to new recommendations released by the CDC.
Vaccines offer excellent (though not complete) protection against moderate to severe disease, hospitalization, and death. Early evidence suggests you're also less likely to infect others once you've been vaccinated, but we don't know that for certain, and it's unlikely that the risk of transmission will be zero. We also don't know how vaccines affect asymptomatic transmission — the ability to infect others if you are infected but aren't experiencing symptoms. That's why it's important to continue taking precautions. And it's why you need to think about risk not just to yourself, but also to others, when you're making decisions.
After vaccination, you can feel safer going to places like the pharmacy or grocery store. If you're a healthcare or essential worker, you can feel safer going to work. But you must still be masked and physically distancing, to help protect others.
As more of your family and friends start to get vaccinated, you can start socializing in person again. Many people are eager to visit older family members; it'll be much safer to do so once you're all vaccinated. The CDC says that small indoor gatherings with others who are also fully vaccinated are okay, and do not require masks or distancing.
Fully vaccinated people may consider gathering indoors, without additional precautions, with unvaccinated people from a single household who are at low risk for severe COVID-19. (But when weather permits, why not meet outdoors or at least keep the windows open?)
For now, it's still best to avoid medium to large indoor gatherings, and large indoor spaces like movie theaters and malls. Continue to avoid unnecessary travel.
It may be tempting to return to pre-pandemic life as soon as you're vaccinated, but be patient. Slowly but surely, we will return to the things we miss.
What side effects can I expect from the COVID vaccine?
Minor side effects are common after COVID-19 vaccination. Almost everyone experiences arm pain at the injection site. Other symptoms can include low grade fever, body ache, chills, fatigue, and headache.
You can expect to feel better within 24 to 48 hours. Some people feel too unwell to go to work or perform their usually daily activities during this period. Contact your doctor if your symptoms have not improved by the third day.
Moving your sore arm around may help to relieve discomfort. If you have a fever, drink plenty of fluids. Over-the-counter pain relievers like ibuprofen or acetaminophen can also help with fever, pain, and other discomfort. However, it's best to not take a pain reliever right before getting your shot, because there is a chance this could blunt your immune response.
The good news: These side effects are a sign that the vaccine is working and that your body is building an antibody response. The currently available vaccines require two shots, and side effects are more likely to occur after the second shot.
I have a severe allergy. Can I get the mRNA COVID-19 vaccine?
There have been rare cases of people having a severe allergic reaction after receiving the mRNA COVID-19 vaccine. As a result, everyone getting an mRNA vaccine in the US must be observed for at least 15 minutes after getting their shot, so they can receive immediate medical treatment if they experience a severe allergic reaction.
Despite the small risk, most people with a history of severe allergy can safely get the mRNA COVID-19 vaccine. This includes people who are allergic to food, pollen, bee stings, and medications taken by mouth. If you have a history of severe allergy, tell the person administering your vaccine. You will be observed for at least 30 minutes, instead of the usual 15 minutes.
If you have a history of allergic reactions to injectable medications or other vaccines, the CDC recommends asking your doctor if you should get one of the currently available mRNA vaccines.
There are some people who should not get an mRNA COVID vaccine. You should not get one if you are allergic to any components of the mRNA vaccine, which include polyethylene glycol (PEG) and polysorbate. And you should not get the second dose of an mRNA vaccine if you had an allergic reaction within the first 30 minutes after receiving the first vaccine dose.
If you have questions regarding the safety of the COVID vaccine for you, your best option is to talk to your doctor.
Are there any groups of people who should not get the mRNA COVID-19 vaccine?
There are only a few groups of people who should not get the mRNA vaccine. They include people who
- are allergic to any components of the mRNA vaccine, which include polyethylene glycol (PEG) and polysorbate
- had an allergic reaction within the first 30 minutes after receiving the first dose of an mRNA COVID-19 vaccine.
If you have a history of allergic reactions to other (non-COVID) vaccines or to injectable medications, ask your doctor if it is safe for you to get one of the currently available mRNA vaccines.
People with weakened immune systems, including those with autoimmune conditions and those taking immune-suppressing treatment, are at increased risk for severe COVID illness. People in these groups can get an mRNA vaccine. However, there may be other safety considerations. If you fall into this category, talk to your doctor about your individual risks and benefits.
Finally, it is possible that convalescent plasma or monoclonal antibodies, both of which are used to treat COVID-19, could reduce the effectiveness of the vaccine. If you have received either of these treatments, wait 90 days before getting your vaccine.
Will the COVID-19 mRNA vaccines work against the new coronavirus variants?
Mutations have led to several new, concerning coronavirus variants, including the B.1.1.7 variant, which was first detected in the United Kingdom; the B.1.351 variant, which originated in South Africa; and the P.1 variant, which originated in Brazil. Early evidence suggests that the current mRNA vaccines are effective against the B.1.1.7 variant, but possibly less so against the others.
In laboratory studies, researchers tested the effectiveness of the Pfizer/BioNTech mRNA vaccine against mutations found in the B.1.1.7 and B.1.351 variants. They found that the neutralizing antibodies the patients had created in response to the vaccine blocked the virus containing mutations from the B.1.1.7 variant as effectively as it blocked the unmutated virus. In the lab, the vaccine was less effective at protecting against virus-containing mutations found in the B.1.351 variant. Real-world results have been more promising. All nine COVID-19 cases observed among 800 study participants in South Africa, where the B.1.351 variant is common, occurred in the placebo group. This translates to 100% vaccine effectiveness. These results were announced in a Pfizer/BioNTech press release.
The Moderna vaccine also performed well against the B.1.1.7 variant. However, it was also less effective against the B.1.351 variant; in a laboratory study, the vaccine resulted in fewer neutralizing antibodies being produced against the B.1.351 variant, compared to the unmutated virus and the B.1.1.7 variant.
Neither company has released data regarding the P.1 variant, which shares some of the same mutations as the B.1.351 variant.
More study is needed to see if the laboratory results hold up in real-world conditions.
Both Moderna and Pfizer/BioNTech have announced plans to study variant-specific vaccine boosters, designed to specifically target the B.1.351 variant. In addition, both companies are testing whether a third dose of their existing, FDA-authorized vaccines provide additional protection against variants of concern.
Early laboratory evidence suggests that antibodies created in response to both the Pfizer/BioNTech and Moderna mRNA vaccines are effective against another new variant known as the New York variant, or B.1.526.
It's important to remember that both the Pfizer/BioNTech and Moderna vaccines are extremely effective — 95% and 94.1%, respectively. Even with a drop in effectiveness, they will still provide protection. Moderna has announced that it is looking into potential benefits of adding a booster dose to their two-dose regimen.
What do we know about the Moderna COVID-19 vaccine that the FDA has authorized for emergency use?
On December 18, 2020, the FDA granted emergency use authorization (EUA) to an mRNA COVID-19 vaccine developed by Moderna in collaboration with scientists from the NIH. The vaccine is approved for use in people 18 years and older. This is the second COVID-19 vaccine authorized for use in the US. (The Pfizer/BioNTech vaccine received EUA during the prior week.)
The FDA granted EUA based on their own analysis of efficacy and safety data, as well as on the recommendation made by the Vaccines and Related Biological Products Advisory Committee (VRBPAC). VRBPAC is a group of outside experts in infectious disease, vaccinology, microbiology, immunology, and other related fields.
In briefing documents submitted to the FDA, the Moderna vaccine showed an overall efficacy of 94.1% in preventing COVID-19. This study enrolled 30,400 adults; half received the vaccine, half received a saltwater placebo shot. There were 196 infections among the study participants. Of these, 185 were in the placebo group and 11 were in the vaccine group. All 30 cases of severe COVID occurred in the placebo group, strongly suggesting indicating that the vaccine reduces risk of severe illness.
The vaccine was similarly effective in people older and younger than 65, in men and women, in people with and without medical conditions that put them at high risk for severe illness, and in different racial and ethnic groups.
The most common vaccine side effects were pain at the injection site, fatigue, headache, muscle pain, joint pain, and chills.
This vaccine requires two doses, spaced four weeks apart. In January 2021, the CDC released guidance stating that while the second dose should be administered as close to the recommended four-week interval as possible, it may be scheduled for administration up to six weeks (42 days) after the first dose. We do not yet know how long immunity from this vaccine will last.
The Moderna vaccine contains synthetic messenger RNA (mRNA), genetic material that enters human cells and instructs them to produce the spike protein found on the surface of the SARS-CoV-2 virus. The body recognizes the spike protein as an invader and produces antibodies against it. Soon after, the cell breaks down the mRNA into harmless pieces. If the antibodies later encounter the actual virus, they are ready to recognize and destroy it before it causes illness.
Unlike the Pfizer vaccine, which requires ultracold storage, the Moderna vaccine can be stored at normal freezer temperatures. This may allow for wider distribution to pharmacies and other facilities that are not equipped for ultracold storage.
What do we know about the Pfizer/BioNTech COVID-19 vaccine that the FDA has authorized for emergency use?
On December 11, 2020, the FDA granted emergency use authorization (EUA) to an mRNA COVID-19 vaccine developed by Pfizer and BioNTech. The vaccine is approved for use in people 16 years and older. This is the first COVID-19 vaccine authorized for use in the US.
The FDA granted EUA based on their own analysis of efficacy and safety data as well as on the recommendation made by the Vaccines and Related Biological Products Advisory Committee (VRBPAC) on December 10th. VRBPAC is a group of outside experts in infectious disease, vaccinology, microbiology, immunology, and other related fields.
Results from the Pfizer/BioNTech vaccine trial were published in the New England Journal of Medicine. The data showed that the vaccine reduced the risk of COVID-19 by 95%. The trial enrolled nearly 44,000 adults, each of whom got two shots, spaced three weeks apart; half received the vaccine and half got a placebo (a shot of saltwater). Of the 170 cases of COVID-19 that developed in the study participants, 162 were in the placebo group and eight were in the vaccine group. Nine of the 10 severe COVID cases occurred in the placebo group, suggesting that the vaccine reduced risk of both mild and severe COVID.
According to the NEJM article, the vaccine was similarly effective in study participants of different races and ethnicities, body weight categories, presence or absence of coexisting medical conditions, and ages (younger and older than 65). It's worth noting that the FDA felt comfortable authorizing the vaccine for 16- and 17-year-olds, even though the number of teens enrolled in the study was small.
None of the study participants experienced serious side effects. However, most did have pain at the injection site. Also, about half of those receiving the vaccine reported mild to moderate fatigue or headache or both. Chills and fever were also fairly common. Symptoms almost always resolved within 24 to 48 hours.
This vaccine requires two doses, spaced three weeks apart. In January 2021, the CDC released guidance stating that while the second dose should be administered as close to the recommended three-week interval as possible, it may be scheduled for administration up to six weeks (42 days) after the first dose. Although the vaccine appears to provide reasonable protection after the first dose, it provides stronger protection after two doses. We do not yet know how long immunity from this vaccine will last.
The Pfizer/BioNTech vaccine is an mRNA vaccine. The vaccine contains synthetic messenger RNA (mRNA), genetic material that contains instructions for making proteins. Inside the body, the mRNA enters human cells and instructs them to produce a single component of the SARS-CoV-2 virus — the "spike" protein found on the virus's surface. The body recognizes the spike protein as an invader and produces antibodies against it. If the antibodies later encounter the actual virus, they are ready to recognize and destroy it before it causes illness. mRNA vaccines must be stored at very cold temperatures; improperly stored vaccines can become inactive.
Healthcare workers and residents and staff of long-term care facilities will be the first to get the vaccine.
What do we know about Johnson & Johnson's adenovirus vaccine?
On February 27, 2021, the FDA granted emergency use authorization (EUA) for Johnson & Johnson's single-shot adenovirus vaccine, following the recommendation from the FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC). The vaccine is authorized for use in people 18 years and older.
However, on April 13, 2021, the FDA and CDC jointly recommended pausing use of the Johnson & Johnson COVID-19 vaccine until the agencies can investigate the cases of an extremely rare but serious type of blood clot that were reported in six women who received the Johnson & Johnson vaccine.
The EUA was based on clinical trial data that found the vaccine to be 85% effective at preventing severe disease, including prevention of hospitalization and death due to COVID-19. The vaccine also appeared to be more than 80% effective at preventing severe COVID disease in South Africa, where the B.1.351 variant is more common. Early data suggest the vaccine may also result in milder illness with fewer symptoms in those who develop COVID-19 after vaccination.
Johnson & Johnson's ongoing phase 3 randomized, double-blind, placebo-controlled clinical trial, is designed to evaluate the safety and effectiveness of the vaccine compared to placebo in adults ages 18 and older. The study enrolled nearly 45,000 participants; half received the COVID-19 vaccine and the other half received a placebo.
Protection was generally consistent across race and age groups. Worldwide, the study participants were 59% White/Caucasian, 45% Hispanic and/or Latinx, 19% Black/African American, 9% Native American, and 3% Asian. In addition, 34% of participants enrolled in the study were over age 60, and 41% had at least one medical condition that put them at increased risk for severe COVID illness. Results suggest the vaccine may be less effective in people 60 years and older with comorbid conditions like diabetes or heart disease; however, no COVID-related deaths or medical interventions occurred in this population of vaccinated study participants.
Common vaccine side effects included mild to moderate pain at the site of injection, headache, fatigue, and muscle aches. A few rare, unexpected side effects also occurred: 15 vaccinated study participants and 10 volunteers who got a placebo developed conditions related to blood clots; six vaccinated volunteers (but none in the placebo group) developed a ringing in the ears called tinnitus; and there were eight cases of hives among vaccine recipients, compared to three among those who received placebo.
The Johnson & Johnson vaccine uses a modified, harmless form of a human common-cold adenovirus to deliver into the body the genetic instructions for making the coronavirus spike protein. Human cells use the instructions to make copies of the spike protein. The body recognizes the spike protein as an invader and produces antibodies against it. If the antibodies later encounter the actual virus, they are ready to recognize and destroy it before it causes illness.
In addition to the advantage of having a one-dose vaccine, the other point in favor of the J&J vaccine is ease of storage. It can be safely refrigerated for months and frozen for even longer, unlike the mRNA vaccines, which must be frozen (one at ultracold temperatures).
What do we know about the AstraZeneca adenovirus COVID-19 vaccine?
An analysis of Phase 3 clinical trial data suggests that the COVID-19 vaccine developed by AstraZeneca and the University of Oxford is effective and safe. AstraZeneca presented interim results in a press release on March 22, 2021. Within a day, however, the National Institutes of Allergy and Infectious Diseases (NIAID) released a statement expressing concern that AstraZeneca's analysis may contain outdated information and may provide "an incomplete view of the efficacy data." On March 25th, AstraZeneca released a new analysis, also in a press release, that included more recent trial data. The FDA will have the opportunity to carefully examine and conduct its own analysis of all of the trial data when AstraZeneca applies for emergency use authorization (EUA), which is expected to happen in the coming weeks.
According to AstraZeneca's most recent analysis, vaccine recipients were 76% less likely to develop symptomatic COVID infection than those who received a placebo. The vaccine was also 100% effective for protecting against severe COVID and hospitalization; there were eight cases of severe COVID in the placebo group, compared to none in the vaccine group.
The analysis looked at results from a trial of about 32,000 participants from the US, France, Chile, and Peru. Two-thirds of the study participants were randomly selected to received two doses of the vaccine, spaced four weeks apart. The remaining one-third of participants got a saltwater placebo.
The trial did not raise any safety concerns. However, the European Medicines Agency (EMA) conducted a specific review of blood clots — a cause of concern in Europe, where the vaccine is already available. On April 7, 2021, the EMA concluded that there is a link between the AstraZeneca vaccine and very rare cases of unusual blood clots. However, the EMA went on to say that the overall benefits of the vaccine in preventing COVID-19 outweigh the risks of side effects. Most cases reviewed by the EMA occurred within two weeks of vaccination in women younger than 60.
The vaccine was 85% effective in people ages 65 and older. It was also similarly effective across people of different ethnicities.
One important question is how effective this vaccine is against SARS-CoV-2 variants. A NEJM study reporting results from the South Africa arm of the AstraZeneca trial concluded that the AstraZeneca vaccine did not protect against mild to moderate COVID-19 caused by the B.1.351 (South Africa) variant.
The AstraZeneca vaccine uses a modified, harmless form of a chimpanzee common-cold adenovirus to deliver the genetic code for the coronavirus spike protein into the body. Human cells read the code and make the spike protein, prompting the immune system to produce antibodies against it, and preparing the body for attack if it later encounters SARS-CoV-2.
Johnson & Johnson's COVID-19 vaccine, which received EUA in February 2021, is also an adenovirus vaccine. Both the AstraZeneca and Johnson & Johnson adenovirus vaccines can be safely refrigerated for several months, unlike the mRNA vaccines, which must be frozen.
Should I get the COVID-19 vaccine if I already had COVID-19?
Even people who have already gotten sick with COVID-19 may benefit from the vaccine, according to the CDC.
Here's what we know. COVID-19 can lead to serious illness and long-term complications, even in younger people and those without underlying medical conditions. We also know that it's possible for someone who has already had COVID-19 to be re-infected, though this is not common.
On the other hand, we don't know how long natural immunity to COVID-19 — the protection that results from having been sick — lasts. It's not clear if the strength or duration of natural immunity varies based on the severity of the initial illness. We also don't know how long immunity conferred by vaccines lasts.
During the initial deployment of the vaccine to front line workers and people in long-term care facilities like nursing homes, people eligible for the vaccine will get it regardless of whether or not they were previously infected. They are not being tested for antibodies prior to vaccination.
As scientists learn more about natural immunity after COVID illness, vaccination criteria based on the presence of antibodies may play a role in the future.
Will the COVID vaccine prevent me from infecting others?
Increasing evidence suggests that a person who has been vaccinated is less likely to infect others.
Two studies released in February pointed in this direction. The first study looked at viral load — the amount of SARS-CoV-2 virus in a person's nose and throat, which can be spread to others. The study found that the higher a person's viral load, the more likely they were to spread the infection; the lower a person's viral load, the less likely they were to spread the infection. Results from the second study suggested that people who became infected with SARS-CoV-2 after getting a COVID vaccine had a lower viral load than people who were infected but had not had a COVID vaccine. Taken together, the studies suggest that the COVID vaccine protects against both infection and transmission.
A study published in March 2021 showed that people who received an mRNA vaccine had significantly less risk of asymptomatic infection than people who were unvaccinated. This is important because people who are infected but never go on to develop symptoms are responsible for an estimated 24% of SARS-CoV-2 transmission.
For now, even if you have been vaccinated, you should continue wearing masks in public and following other CDC recommendations to protect yourself and others.
Once I get the COVID-19 vaccine, can I stop taking other precautions?
Early, emerging evidence suggests that the COVID-19 vaccine may reduce the chances that you will infect others. But more research is needed to know for certain if the vaccine reduces transmissibility. That's why, at least for now, you need to continue wearing a mask and physically distancing from others, even after you are vaccinated.
What needed to happen before the FDA authorized a vaccine for COVID-19?
A successful COVID-19 vaccine had to safely and effectively stimulate the body's immune system to create antibodies that protect against the COVID-19 coronavirus. On December 11, 2020, the FDA granted emergency use authorization (EUA) to an mRNA COVID-19 vaccine developed by Pfizer and BioNTech. One week later, the FDA granted EUA to another mRNA COVID-19 vaccine, this one developed by Moderna. On February 27, 2021, the FDA granted EUA to an adenovirus vaccine developed by Johnson & Johnson. A number of other, possible COVID-19 vaccines are in various stages of development and testing.
Approval of a vaccine requires completion of the following steps:
- Pre-clinical testing: Animals are infected with the virus. Scientists study their immune response to see what aspects of the immune response might be critical for protection. Normally, a vaccine is first tested in animals. However, in the setting of a pandemic such as this one, the animal testing stage can be skipped.
- Phase 1 trials: A vaccine is tested in small groups of people to determine what dose safely and consistently stimulates the immune system. At this stage, scientists don't yet know if the immune response triggered by the vaccine will protect against the virus.
- Phase 2 trials: The vaccine is given to hundreds or thousands of people. Scientists continue to focus on whether the vaccine is safe and produces a consistent immune response.
- Phase 3 trials: These trials typically enroll tens of thousands of people. This is the first phase that involves a placebo group. It compares the number of people who get sick in the vaccine group to the number of people who get sick in the placebo group. This is the only phase that can show whether or not the immune response triggered by the vaccine actually protects against infection in the real world.
What are mRNA vaccines and how do they work to help prevent COVID-19?
mRNA, or messenger RNA, is genetic material that contains instructions for making proteins. mRNA vaccines for COVID-19 contain synthetic mRNA. Inside the body, the mRNA enters human cells and instructs them to produce the "spike" protein found on the surface of SARS-CoV-2, the virus that causes COVID-19. The body recognizes the spike protein as an invader, and starts producing antibodies against it. Soon after, the cell breaks down the mRNA into harmless pieces If the antibodies later encounter the actual virus, they are ready to recognize and destroy it before it causes illness.
Two mRNA vaccines, one created by Pfizer and BioNTech and another developed by Moderna, were granted emergency use authorization (EUA) by the FDA in December 2020.
Video Credit: Justin Saglio/Harvard Public Affairs & Communications
Could an mRNA vaccine change my DNA?
An mRNA vaccine — the first COVID-19 vaccine to be granted emergency use authorization (EUA) by the FDA — cannot change your DNA.
mRNA, or messenger RNA, is genetic material that contains instructions for making proteins. mRNA vaccines for COVID-19 contain man-made mRNA. Inside the body, the mRNA enters human cells and instructs them to produce the "spike" protein found on the surface of the COVID-19 virus. Soon after a cell makes the spike protein, the cell breaks down the mRNA into harmless pieces. At no point does the mRNA enter the cell's nucleus, which is where our genetic material (DNA) lives.
The immune system recognizes the spike protein as an invader and produces antibodies against it. If the antibodies later encounter the actual virus, they are ready to recognize and destroy it before it causes illness.
I am pregnant and plan to eventually breastfeed my baby. Is it safe for me to get a mRNA COVID-19 vaccine?
The CDC, American College of Obstetrics and Gynecology (ACOG), and Society for Maternal-Fetal Medicine agree that the new mRNA COVID-19 vaccines (Pfizer/BioNTech and Moderna) should be offered to pregnant and breastfeeding individuals. However, the World Health Organization (WHO) recommends against use of either mRNA vaccine in pregnant women, unless the benefit to an individual outweighs the potential vaccine risks. Experts, including the WHO, believe it is most likely safe to get an mRNA COVID-19 vaccine if you're breastfeeding. As always, your own doctor is in the best position to advise you based on your personal health risks and preferences.
Here are some factors to consider. First, although the actual risk of severe COVID-19 illness and death among pregnant individuals is very low, it is higher when compared to nonpregnant individuals from the same age group. In addition, research suggests that having COVID-19 might increase risk for premature birth, particularly for those with severe illness. Transmission of the virus from mother to baby during pregnancy is possible, but it appears to be a rare event.
Early mRNA vaccine trials did not deliberately include pregnant individuals. However, subsequent trials have enrolled women who are pregnant. Results from a small study that compared vaccine efficacy in pregnant and non-pregnant women were published in the American Journal of Obstetrics and Gynecology. The study found that mRNA vaccines effectively produce antibodies that protect against SARS-CoV-2 in women who are pregnant or breastfeeding, and that this immunity is passed from mother to newborn through the placenta and breast milk.
mRNA vaccines do not contain any virus, so they cannot cause COVID-19 in a woman or her baby. And our bodies quickly break down and eliminate mRNA particles used in the vaccine, so they are unlikely to reach or cross the placenta.
When will children be able to get the COVID-19 vaccine?
Pfizer/BioNTech and Moderna are already conducting age de-escalation studies, in which the vaccines are tested in groups of children of descending age. Johnson & Johnson plans to do the same. Currently, the Pfizer/BioNTech COVID-19 vaccine is authorized for use in children 16 years and older, while the Moderna and Johnson & Johnson vaccines are authorized for people 18 years and older.
In March 2021, Pfizer/BioNTech announced promising results for a Phase 3 trial testing its vaccine in children ages 12 to 15. The trial enrolled 2,260 adolescents; half received the mRNA vaccine, the other received a saltwater placebo. The antibody response in the vaccinated adolescent group was even stronger than that in vaccinated 16- to 25-year-olds enrolled in an earlier study. In addition, a total of 18 symptomatic cases of COVID-19 were reported during the trial, all in the placebo group. Vaccine-related symptoms were mild and comparable to older groups enrolled in earlier studies. The results were announced in a press release, not in a peer-reviewed, published study. Pfizer/BioNTech has submitted their data to the FDA with a request to expand emergency use authorization to children ages 12 to 15. The company has also started testing the vaccine in children younger than 12 years.
Moderna is conducting two vaccines studies — one in children ages 12 to 17, the other in children between the ages of 6 months and 12 years.
The age de-escalation studies are done to confirm that the vaccines are safe and effective for each age group. They also identify the optimal dose, which must be effective, but with tolerable side effects.
The age de-escalation studies are smaller than the adult trials; rather than recruiting tens of thousands of participants, they will recruit 2,000 to 3,000 participants within each age group. As in the adult trials, some children in each trial will get a placebo.
The FDA will review data from the de-escalation trials to decide whether to authorize the vaccines for each age group.
Who is eligible to get the COVID-19 vaccine, and who is next?
The CDC issued guidance for vaccine rollout based on recommendations from the Advisory Committee on Immunization Practices (ACIP).
Healthcare workers and residents and staff of long-term care facilities became the first group in the US to start getting the COVID-19 vaccine in mid-December 2020. The CDC recommended that adults ages 75 and older and frontline essential workers be vaccinated next, to be followed by adults ages 65 to 74, people ages 16 to 64 with medical conditions that put them at high risk for severe COVID-19, and remaining essential workers. Eventually, anyone who has not been vaccinated will be eligible for a COVID vaccine.
States across the US are at different stages of their vaccine rollouts.
What are the promising vaccines for COVID-19 under investigation?
Around the world, there are currently over 70 different COVID-19 vaccines in various stages of testing and development: phase 1 (safety), phase 2 (optimal dose, schedule, and proof of concept), and phase 3 (effectiveness, side effects) trials in humans.
In December 2020, the FDA granted emergency use authorization (EUA) to two COVID-19 vaccines, one developed by Pfizer/BioNTech and another developed by Moderna. These vaccines use a type of molecule called messenger RNA (mRNA) that can be mass-manufactured very rapidly. In these vaccines, mRNA induces human cells to make a protein that looks just like the spike protein that studs the surface of the coronavirus and enables it to enter human cells. The body recognizes the spike protein as an invader, and produces antibodies against it. If the antibodies later encounter the actual virus, they are ready to recognize and destroy it before it causes illness.
In February 2021, the FDA granted EUA to Johnson & Johnson's adenovirus vaccine. However, on April 13, 2021, the FDA and CDC jointly recommended pausing use of the Johnson & Johnson COVID-19 vaccine until the agencies can investigate the cases of an extremely rare but serious type of blood clot that were reported in six women who received the Johnson & Johnson vaccine.
The Johnson & Johnson vaccine uses a modified, harmless form of a human common-cold adenovirus to deliver into the body the genetic instructions for making the coronavirus spike protein. Human cells use the instructions to make copies of the spike protein. The body recognizes the spike protein as an invader and produces antibodies against it. Clinical trial data found the vaccine to be 85% effective at preventing severe disease, including prevention of hospitalization and death due to COVID-19. Early data suggest the vaccine may also result in milder illness with fewer symptoms in those who develop COVID-19 after vaccination.
Two other vaccine approaches are also showing promise.
- A vaccine created by AstraZeneca and the University of Oxford uses a modified, harmless form of a chimpanzee common-cold adenovirus to deliver the genetic code for the coronavirus spike protein into the body. Human cells read the code and make spike protein, which prompts the immune system to produce antibodies against it, preparing the body to attack the SARS-CoV-2 virus if it later infects the body. The company released promising interim phase 3 trial results in a press release in March 2021. However, on April 7, 2021, the European Medicines Agency announced a link between the AstraZeneca vaccine and very rare cases of unusual blood clots, similar to the clotting issue reported with the Johnson & Johnson vaccine. The EMA went on to say that the overall benefits of the vaccine in preventing COVID-19 outweigh the risks of side effects.
- Another vaccine, created by Novavax, contains manufactured spike protein and an adjuvant; together, they stimulate an immune response. In a press release, Novavax released interim analysis of phase 3 clinical trial results, which found the vaccine to be 89.3% effective against symptomatic mild, moderate, and severe COVID-19. It was slightly more effective against the common COVID-19 variant and slightly less effective (85.6%) against the B.1.1.7 variant that originated in the United Kingdom. A smaller Phase 2 study conducted in South Africa showed the vaccine to be less effective (about 60%) against the B.1.351 variant that originated there. This vaccine requires two doses.
A central question for COVID-19 vaccines will be how long protection might last.
- Fully vaccinated against COVID-19? So, what can you safely do?
- You got the COVID-19 vaccine? I have vaccine envy
- My COVID-19 vaccine story –– and what happened next
- Why won't some health care workers get vaccinated?
- COVID-19 vaccines: Safety, side effects –– and coincidence
- Wondering about COVID-19 vaccines if you're pregnant or breastfeeding?
- Why are mRNA vaccines so exciting?
- Vaccines for COVID-19 moving closer
Visit our Coronavirus Resource Center for more information on coronavirus and COVID-19.
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