COVID-19 vaccines

What you need to know before getting vaccinated

The FDA has authorized two COVID-19 vaccines, which were found to be safe and effective in clinical trials. 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.

Is there a vaccine available 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. This was the first COVID-19 vaccine authorized for use in the US. One week later, the FDA granted EUA to an mRNA COVID-19 vaccine developed by Moderna.

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?

Early evidence suggests that the Pfizer/BioNTech mRNA vaccine is effective against the new coronavirus variants. Testing of the Moderna mRNA vaccine against the new variants is underway.

The two new variants are more contagious than previous SARS-CoV-2 variants, but they do not appear to be deadlier. One, called B.1.1.7, was first detected in the United Kingdom. The other, called B.1.351, originated in South Africa. Both variants have now been detected in countries around the globe.

Both variants contain mutations on the virus's spike protein. Spike proteins on the surface of the SARS-CoV-2 virus bind to and allow the virus to enter human cells. Interestingly, both variants share a key mutation (called N501Y) on the spike protein, which allows the virus to bind more tightly to human cells. This mutation makes the new variants more contagious than previous SARS-CoV-2 variants.

To test the effectiveness of the Pfizer/BioNTech mRNA vaccine against the new variants, researchers created a virus with the N501Y mutation. They then took blood samples from 20 participants enrolled in their vaccine trial and exposed the samples to the mutated virus. The participants' blood contained human cells as well as antibodies made in response to the Pfizer/BioNTech vaccine. They found that the antibodies blocked the mutated virus from infecting human cells as effectively as it blocked the virus without the mutation.

More study is needed to see if these results hold up in real world conditions. It's also not known how long this protection may last, and whether the vaccines will work against other mutations found in these variants.

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. 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. 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.

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?

The answer is, we don't know.

Clinical trials of the Pfizer/BioNTech and Moderna vaccines found that both do a good job preventing symptomatic COVID-19 disease, including severe COVID-19. However, the trials did not measure whether a person who is vaccinated is less likely to spread the virus to someone else.

It's possible that the vaccines protect against COVID-19 disease by preventing a person from becoming infected in the first place. However, it's also possible that the vaccine protects a person from COVID-19 illness, but does not prevent a person from becoming infected. In other words, a vaccinated person may have replicating virus in their nose and throat even if they are protected from becoming sick.

But does that mean that you have enough virus in your nose and throat to infect someone else? Not necessarily. It's possible that the immune response triggered by the vaccine, which protects you from becoming sick, also reduces the amount of virus in your nose and throat to a point where you are unlikely to spread it to someone else. But we need more research to know for sure.

The bottom line? If you're among the first groups of people to get vaccinated, it's best to continue wearing masks and maintaining physical distance in order to protect others who haven't yet gotten the vaccine.

Once I get the COVID-19 vaccine, can I stop taking other precautions?

The vaccine will protect you from getting sick, but it may not prevent you from infecting others. That's why, at least for now, you should continue wearing a mask and physically distancing from others, even after you get your shot.

Clinical trials of the Pfizer/BioNTech and Moderna vaccines found that both do a good job preventing symptomatic COVID-19 disease, including severe COVID-19. However, the trials did not measure whether a person who is vaccinated is less likely to spread the virus to someone else.

It's possible that the vaccines protect against COVID-19 disease by preventing a person from becoming infected. However, it's also possible that the vaccine protects a person from getting sick but does not prevent the virus from replicating in that person's nose and throat.

Does that mean there's enough virus in your nose and throat to infect someone else? Not necessarily. But we need more research to know for sure.

Where does that leave us? If you're among the first groups of people to get vaccinated, it's best to continue wearing masks and maintaining physical distance in order to protect others who haven't yet gotten the vaccine.

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. At least two other vaccine candidates are close behind, and more 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.

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. But there is a lot we still do not know about the safety of the vaccines in these populations, and 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.

mRNA vaccine trials did not deliberately include pregnant individuals, so our knowledge regarding the safety of mRNA COVID-19 vaccines during pregnancy is limited. In animal studies, mRNA vaccines did not affect fertility or cause any problems with pregnancy. 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. On the other hand, the immunity that a woman generates from vaccination can cross the placenta, and may help to keep the baby safe after birth.

Experts also believe it is most likely safe to get an mRNA COVID-19 vaccine if you're breastfeeding, although breastfeeding people were not included in the vaccine trials. When a person gets vaccinated while breastfeeding, their immune system develops antibodies that protect against COVID-19. These antibodies can be passed through breast milk to the baby and are likely to help protect against infection.

What are adenovirus vaccines? What do we know about adenovirus vaccines that are being developed for COVID-19?

Adenoviruses can cause a variety of illnesses, including the common cold. They are being used in two leading COVID-19 vaccine candidates as capsules (the scientific term is vectors) to deliver the coronavirus spike protein into the body. The spike protein 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.

In December 2020, AstraZeneca published promising results of an adenovirus-based vaccine that it developed with researchers at the University of Oxford. The study was published in the journal The Lancet.

The Lancet analysis of vaccine efficacy was based on 11,636 adult study participants. Of these, 4,440 participants received a full dose of the coronavirus vaccine, followed four weeks later by another full dose. Nearly 1,400 participants received a half dose of the coronavirus vaccine, followed four weeks later by a full dose. The control group received a meningitis vaccine, followed by a second meningitis vaccine or a placebo (a salt water shot). There were 131 documented cases of COVID-19, all of which occurred at least two weeks after the second shot.

The coronavirus vaccine reduced the risk of COVID-19 by an average of 70.4%, compared to the control group. Surprisingly, the half dose/full dose vaccine combination was more effective, reducing risk of COVID-19 by 90%. The full dose combination reduced risk by 62%. None of the participants who received the coronavirus vaccine developed severe COVID-19 or had to be hospitalized. There was also a reduction in asymptomatic cases.

Most study participants were between the ages of 18 and 55, and white. In addition, the study participants were healthy or had stable underlying medical conditions. More data is needed to understand how effective this vaccine is in people older than 55, people of color, and people with underlying medical conditions. This vaccine is in clinical trials around the world, including the US. But this analysis was based on data from the United Kingdom and Brazil.

The adenovirus used in the AstraZeneca/University of Oxford vaccine is a weakened, harmless form of a chimpanzee common-cold adenovirus. This vaccine can be safely refrigerated for several months.

Who will get the first COVID-19 vaccines and who is next?

In mid-December, 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. The CDC has recommended that adults age 75 years and older and frontline essential workers be vaccinated next. They will be followed by adults aged 65 to 74, people aged 16 to 64 with medical conditions that put them at high risk for severe COVID-19, and remaining essential workers.

State and local authorities are not obligated to follow the CDC's recommendations; they may reprioritize the order in which they distribute the vaccines at their discretion.

There are about 21 million healthcare workers in the US, doing a variety of jobs in hospitals and outpatient clinics, pharmacies, emergency medical services, and public health. Another three million people reside or work in long-term care facilities, which include nursing homes, assisted-living facilities, and residential care facilities. COVID-19 has taken a heavy toll on residents of long-term care facilities. Frontline essential workers are those who cannot work from home and who may not be able to physically distance while working. They include first responders such as firefighters and police, teachers and day care workers, postal workers, and people who work in grocery stores.

The CDC's guidance is based on a recommendation from the Advisory Committee on Immunization Practices (ACIP), made up of experts in vaccinology, immunology, virology, public health, and other related fields. Their work is not limited to the COVID-19 vaccine; they broadly advise the CDC on vaccinations and immunization schedules.

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.

Two other vaccine approaches are also showing promise.

  • A hybrid vaccine created by AstraZeneca and the University of Oxford uses a modified, harmless form of a chimpanzee common-cold adenovirus to deliver the coronavirus spike protein into the body. The spike protein 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 published promising phase 3 trial results in The Lancet in December 2020.
  • Another hybrid vaccine uses a human common-cold adenovirus to deliver the coronavirus spike protein into the body. That platform was developed by Harvard Medical School scientists in collaboration with Johnson and Johnson. This vaccine is in phase 3 trials.

A central question for COVID-19 vaccines will be how long protection might last.

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