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COVID-19 vaccines

May 20, 2022

What you need to know about COVID-19 vaccines

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The FDA has granted full approval to two COVID-19 vaccine and has authorized one other. As time passes, we will learn more about how long protection from vaccines and boosters lasts, and whether vaccinations will continue to protect against emerging variants. Vaccines remain the key for an end to this pandemic.

Visit our Coronavirus Resource Center for more information on coronavirus and COVID-19.

Do COVID-19 vaccines work against the newer variants?

mRNA COVID-19 vaccines have not protected as well against infection with Omicron as they did against previous SARS-CoV-2 variants. However, the vaccines continue to significantly reduce the chance of severe symptoms, hospitalization, and death, especially for people who have received a booster dose.

Research published in MMWR looked at the medical records of nearly 88,000 people across the US hospitalized with COVID-like symptoms between late August 2021 and early January 2022, which included periods during which both the Delta and Omicron variants were predominant. The data showed that full vaccination plus a booster was 94% effective in protecting against hospitalization with the Delta variant and 90% effective in protecting against hospitalization with the Omicron variant. Protection against hospitalization dropped significantly in people who had gotten their second vaccine dose more than six months prior and who had not gotten a booster dose.

Protection against severe disease and hospitalization in people who are vaccinated compared to those who are unvaccinated is striking. Additional data published by the CDC showed that unvaccinated Americans ages 50 to 64 years were 44 times more likely to be hospitalized than those who were vaccinated and boosted. Unvaccinated Americans ages 65 and older were 49 times more likely to hospitalized than their vaccinated and boosted counterparts.

How might boosters help? Booster-generated antibodies are not more specific to the Omicron variant. But the sheer increase in antibody levels helps enhance our immunity.

But vaccines do more than generate antibodies. They also stimulate other parts of the immune response, including T cells, which attack infected cells and recruit other immune cells to protect against severe illness. The part of the virus targeted by T cells was largely unaffected by mutations in the Omicron variant, so the T cell response in people who are immunized should remain strong.

The evidence reinforces the same important messages. If you are not vaccinated, get vaccinated. If you are eligible for a booster, get boosted. And everyone should continue to mask indoors, avoid crowds, and follow other preventive measures.

Which vaccines has the FDA approved and authorized for COVID-19?

The FDA has granted full approval to the mRNA COVID-19 vaccines developed by Pfizer/BioNTech and Moderna, and has granted emergency use authorization (EUA) to Johnson & Johnson's adenovirus vaccine. In May 2022, the FDA limited use of the Johnson & Johnson vaccine to adults who cannot get, or refuse to get, one of the mRNA vaccines.

The Pfizer/BioNTech vaccine has also been authorized for children ages 5 to 17 years, though children ages 5 to 11 will receive a lower dose.

In addition, booster doses of all three vaccines have been authorized for eligible recipients ages 5 years and older.

Which COVID-19 vaccines are available for children?

The CDC recommends that children ages 5 to 17 years receive the two-dose Pfizer/BioNTech COVID-19 vaccine. Children 12 to 17 years may be vaccinated with the standard Pfizer/BioNTech vaccine, while children ages 5 to 11 years should receive Pfizer/BioNTech’s pediatric vaccine, which is a lower dose (10 micrograms, compared to 30 micrograms for people 12 year and older). For now, only the Pfizer/BioNTech vaccine is authorized in the US for anyone under age 18.

The CDC also recommends a single-dose Pfizer/BioNTech COVID-19 booster shot for children ages 5 years and older, at least five months after getting their second dose of that vaccine.

In addition, the CDC advises that children ages 5 years and older who are moderately to severely immunocompromised should get an additional primary dose of the vaccine 28 days after their second shot. Children who fall into this category and are 5 to 11 years old are eligible for a single booster shot, while those 12 years and older are eligible for a second booster shot.

Who can get a COVID-19 vaccine booster shot?

As of March 2022, the following groups are eligible for a second booster shot:

  • everyone ages 50 years and older who received their first booster (Pfizer/BioNTech, Moderna, or Johnson & Johnson) at least four months ago
  • certain immunocompromised individuals ages 12 years and older who received their first booster at least four months ago.

The CDC is only recommending mRNA vaccines for second boosters, and has stated that a second booster is "…especially important for those 65 and older and those 50 and older with underlying medical conditions that increase their risk for severe disease from COVID-19…"

The CDC recommends a single-dose COVID-19 vaccine booster for all adults ages 18 years and older. Those who initially received the Pfizer/BioNTech or Moderna mRNA vaccine can get their booster five months after their second shot, and those who received an initial dose of the Johnson & Johnson vaccine can get a booster dose two months after their initial vaccine. Adults may select any vaccine for their booster, either the same (homologous) or different (heterologous) than their initial vaccine(s). However, the FDA has limited use of the Johnson & Johnson vaccine to adults who cannot get, or refuse to get, one of the mRNA vaccines.

The CDC also recommends a single-dose Pfizer/BioNTech COVID-19 booster shot for children ages 5 years and older, at least five months after getting their second dose of that vaccine. As of now, individuals in this age group are only authorized to receive the Pfizer/BioNTech vaccine.

Which COVID-19 vaccine booster should I get?

Adults ages 18 years and older may select a COVID-19 vaccine booster that is the same as (homologous) or different than (heterologous) their initial vaccine(s). Only mRNA vaccines (Pfizer/BioNTech and Moderna) have been authorized for second boosters.

The FDA’s mix-and-match authorization makes booster shots less dependent on which vaccines are available and gives people more choices. For example, if you had an unpleasant reaction to your initial vaccine, you could choose a different one for your booster. Or, if you don’t remember which vaccine you started with, you can still get a booster.

Although Johnson & Johnson’s vaccine is still available as an option for the first booster, in May 2022 the FDA limited use of the Johnson & Johnson vaccine to adults who cannot get, or refuse to get, one of the mRNA vaccines, due to concerns about a rare but potentially fatal blood clotting disorder.

The CDC also recommends boosters for children ages 5 to 17 years. Right now, only the Pfizer/BioNTech vaccine is authorized for this age group.

What should I consider before getting a second COVID-19 vaccine booster?

In March 2022, the CDC recommended a second booster shot for anyone ages 50 years and older, as well as certain immunocompromised individuals ages 12 years and older, at least four months after their first booster. The CDC noted: "This is especially important for those 65 and older, and those 50 and older with underlying medical conditions that increase their risk for severe disease from COVID-19, as they are the most likely to benefit from receiving an additional booster dose at this time."

Data from the CDC has shown that the effectiveness of booster shots decreases over time. A study published in MMWR reported that vaccine effectiveness against COVID-related hospitalizations dropped from 91% within two months after a booster dose to 78% four months after a booster dose. Data for this study were collected during the Omicron surge.

A second booster shot may help protect against COVID-related death in older adults, according to a small preprint study from Israel. Of the study participants, all of whom were ages 60 years and older, 232 of the 234,868 people who received one booster shot had a COVID-related death, compared to 92 of the 328,597 people who received two booster shots. That means people who got a second booster were 78% less likely to die than those who got a single booster. This was a significant difference.

The benefits of a second booster for younger, healthier populations are less certain. In a small report published in NEJM, researchers reported only "marginal benefits" of a second booster for middle-aged healthcare workers compared with a single booster. Although the second booster was safe and resulted in a large bump in neutralizing antibodies, vaccine efficacy was low against COVID infections.

Although vaccine effectiveness decreases over time, especially against infection and symptomatic infection, vaccines are still the best way to protect against severe illness. Consider the following factors when thinking about a second booster shot for yourself or a loved one.

  • Age. The risk of severe COVID-related illness increases with age. A second booster increases neutralizing antibody levels, and there is evidence that a second booster protects older people from COVID-related death. The CDC has noted that a second booster is especially important for those 65 years and older.
  • Underlying medical conditions. Immunocompromised individuals and those with certain underlying medical conditions are at increased risk for severe illness, hospitalization, and death due to COVID. The CDC has said that these groups are among those most likely to benefit from a second booster.
  • Timing. There is some evidence that longer intervals between booster doses result in a stronger and longer-lasting immune response. However, that can leave you more vulnerable between booster doses.
  • Goals. Are you trying to reduce your risk of any infection, symptomatic infection, or severe illness and hospitalization? The answer may depend on your age, medical history, and other factors, and could influence how you think about a second booster.
  • What’s next? Omicron-specific mRNA vaccines are in development and may be available later this year.

You can take a variety of precautions against infection in addition to vaccination. These include masking indoors, not eating in indoor restaurants, and avoiding crowded spaces. You can adopt or discard layers of protection depending on COVID risk levels in your community.

Can I get my flu shot at the same time as my COVID-19 booster shot?

According to the CDC, you can get the COVID-19 vaccine and another vaccine, including the flu shot, at the same time. The CDC’s guidance applies to the initial or booster dose of the COVID-19 vaccine.

Getting both vaccines at the same visit does not compromise the effectiveness of either immunization. Side effects are generally the same for vaccines given together or separately. Of course, if you get the shots in different arms, you could experience soreness in both arms.

Many clinics are offering both vaccines at the same visit. It’s best to get your flu shot by the end of October.

I have a weakened immune system. How many doses of the COVID-19 vaccine do I need?

The CDC recommends the following COVID-19 vaccination schedule for moderately to severely immunocompromised people:

  • a three-dose initial mRNA COVID-19 vaccine series for adults and children ages 12 years and older, followed by a first booster shot at least three months after the third shot, and a second booster at least four months after their first booster.
  • a three-dose initial mRNA COVID-19 vaccine series for children ages 5 to 11 years, followed by a booster dose.
  • one dose of an mRNA vaccine at least 28 days after an initial Johnson & Johnson vaccine, followed by a booster dose at least two months after the second shot.

The COVID-19 vaccines, like other vaccines, work by stimulating a person’s immune system to produce antibodies against the virus. If the antibodies later encounter the actual virus, they are ready to recognize and destroy it.

A person with a weakened immune system may not be able to produce a strong enough immune response to even a three-dose COVID mRNA vaccine regimen. This leaves them more likely to have a breakthrough infection, and increases the risk of more severe disease if they do become infected.

A person may have a weakened immune system for a variety of reasons. These include being born with an immunodeficiency, having advanced or untreated HIV, and having a chronic medical condition such as chronic kidney disease or lack of a spleen. Many types of medication also suppress the immune response, including some cancer treatments, TNF blockers, some biologic agents, and high-dose corticosteroids. Talk to your doctor if you think you may qualify for an additional COVID vaccine dose.

In addition to getting vaccinated and boosted, people with a weakened immune system should continue to wear a mask and try to stay six feet apart from others in indoor public places. They should still avoid crowds and poorly ventilated indoor spaces.

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.

Does vaccination protect against long COVID?

Being fully vaccinated with a COVID-19 vaccine does reduce the risk of long COVID. Also called post-COVID-19 syndrome or post-acute sequelae of SARS-CoV-2 infection (PASC), long COVID is the term for symptoms that arise or persist more than 28 days after an initial COVID-19 infection.

Vaccination may reduce the risk of long COVID in two ways. The first is by reducing the risk of becoming infected with COVID in the first place. But what about people who experience breakthrough infections, becoming infected despite being vaccinated?

A study published in The Lancet shows that fully vaccinated people who experience breakthrough infections are about 50% less likely to develop long COVID than people who are infected without having been vaccinated. These results are based on self-reported data submitted via the COVID Symptom Study phone app in the United Kingdom between December 2020 and July 2021.

Have the COVID vaccines effectively protected older adults in the real world?

Two reports published in MMWR in September 2021 found that vaccine protection has declined in older adults. However, vaccinated older adults still enjoy significant protection compared to older adults who are unvaccinated.

One report describes the results of a study looking at the effectiveness of the COVID vaccines (Pfizer/BioNTech, Moderna, and Johnson & Johnson) in preventing COVID-related hospitalization at five Veterans Affairs Medical Centers in the US. It found that vaccines were 80% effective in preventing COVID-related hospitalization in people aged 66 years and older compared to 95% in people aged 18 to 65 years.

The second report is an interim analysis of ongoing data collection from medical sites in nine different states. The vaccines were found to be 89% effective at preventing COVID-related hospitalization in people ages 18 to 74 and 76% in people aged 75 or older. The researchers based their findings on an analysis of 32,867 medical encounters, including visits to hospitals, emergency departments, and urgent care sites. The data collection occurred during a time when Delta was responsible for more than half of infections.

I lost my COVID-19 vaccination record card. What should I do?

When you got your first vaccine dose, you should have received a white, CDC-labeled COVID-19 Vaccination Record Card. The card is filled out by the vaccine provider and indicates which vaccine you got, and when and where you received your shot. When you receive your next vaccine dose or booster, the card is updated with information about the additional shot(s).

 If you lose your card, there are several things you can do:

  • Contact your vaccination provider (for example, your doctor, a pharmacy, a community health center, or a mass vaccination site).
  • Contact your primary care provider (PCP).
  • Contact your state health department’s immunization information system (IIS) by phone or online. Vaccination providers are required to report COVID-19 vaccinations to their IIS and related systems, and many states have systems set up to help you obtain a copy of your COVID vaccination record.
  • If you enrolled in v-safe or VaxText, you can access your vaccination information using those tools.
  • Your state health department may also be able to help.

Once you obtain your vaccine card, take a picture of it, and keep the photo on your phone as a backup copy. You may also be able to get a digital copy of your vaccine record that you can store on your smartphone.

What are breakthrough infections, and why do they happen?

A breakthrough infection is one that occurs after full vaccination or after full vaccination plus a booster dose.

COVID vaccines work by exposing the immune system to the virus’s spike protein, the region of the virus that binds to and allows the virus 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.

But the current vaccines are based on an earlier version of the SARS-CoV-2 virus. And the virus has evolved since they were developed. The Omicron variant, for example, has about 50 mutations, including more than 30 mutations on the spike protein. As the spike protein becomes less recognizable to the immune system, the vaccine becomes less effective at protecting against infections.

Still, vaccines — and especially full vaccination plus a booster — have continued to protect against severe disease, hospitalization, and death in people who do get a breakthrough infection.

That’s because vaccines do more than generate antibodies. They also stimulate other parts of the immune response, including T cells, which attack infected cells and recruit other immune cells to protect against severe illness.

Booster doses also help. Booster-generated antibodies are not more specific to the Omicron variant. But the sheer increase in antibody levels helps enhance our immunity.

I’m vaccinated but got a breakthrough COVID infection. Can I still spread the infection to others?

Yes, you can. That's why the CDC recommends that everyone who tests positive for COVID-19 should isolate from others for at least five days, regardless of their vaccination status.

    The FDA has granted full approval to the Pfizer/BioNTech and Moderna COVID-19 vaccines. How is approval different from emergency use authorization?

    The FDA has granted full approval to the Pfizer/BioNTech COVID-19 mRNA vaccine for use in people ages 16 years and older, and to the Moderna COVID-19 mRNA vaccine for use in people ages 18 years and older. (Children ages 5 to 15 years will continue to use the Pfizer/BioNTech vaccine under emergency use authorization, or EUA, status.)

    For both vaccines, the transition from EUA status to full licensure was based on additional data and longer follow-up showing that the vaccines met certain safety, effectiveness, and manufacturing quality standards. Safety data will continue to be collected and monitored.

    Before granting full approval, the FDA also inspected vaccine manufacturing facilities to ensure vaccine quality. Full approval gives doctors some leeway to prescribe the vaccine for "off-label" use. The Pfizer/BioNTech vaccine can now be marketed under the brand name Comirnaty. The Moderna vaccine will be marketed under the name Spikevax.

    EUA status may be granted by the FDA during public health emergencies when they determine that the known and potential benefits of a medical product — in this case, the COVID-19 vaccine — outweigh the known and potential risks.

    What do we know about Pfizer/BioNTech's mRNA COVID-19 vaccine?

    In August 2021, the FDA granted full approval to the Pfizer/BioNTech COVID-19 mRNA vaccine for use in people ages 16 years and older. This vaccine requires two doses, spaced three weeks apart. The Pfizer/BioNTech vaccine has also been authorized for children ages 5 to 15 years; children ages 5 to 11 will receive a lower dose. In addition, a single-dose Pfizer/BioNTech COVID-19 booster shot has been authorized for eligible recipients ages 5 years and older, and a second booster dose has been authorized for eligible recipients ages 12 years and older. The CDC advises that anyone age 5 years and older who is moderately to severely immunocompromised should get an additional primary dose of the vaccine 28 days after their second shot, as well as one or more booster shots as appropriate.

    The FDA granted its original 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.

    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.

    What do we know about Moderna's COVID-19 vaccine?

    In January 2022, the FDA granted full approval to Moderna's COVID-19 mRNA vaccinefor use in people ages 18 years and older. This vaccine requires two doses, spaced four weeks apart. The vaccine is approved authorized for use in people 18 years and older. In August 2021, the FDA authorized a third dose of mRNA vaccine (Moderna or Pfizer/BioNTech) for certain people with a weakened immune response. The Moderna vaccine may also be given to adults as a booster shot.

    The transition from emergency use authorization (EUA) status to full licensure for the Moderna vaccine was based on additional data and longer follow-up showing that the vaccine met certain safety, effectiveness, and manufacturing quality standards. Safety data will continue to be collected and monitored. Before granting full approval, the FDA also inspected vaccine manufacturing facilities to ensure vaccine quality. The Moderna vaccine will be marketed under the brand name Spikevax.

    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 Johnson & Johnson's adenovirus COVID-19 vaccine?

    In May 2022 the FDA limited use of Johnson & Johnson's COVID-19 vaccine to adults who cannot get, or refuse to get, one of the mRNA vaccines.

    The FDA made the decision because of concerns about a rare, but potentially fatal, blood-clotting disorder.

    The blood clots in question involve blood vessels in the brain, lungs, abdomen, and legs, and are accompanied by low levels of blood platelets. This combination is referred to as thrombosis and thrombocytopenia syndrome, or TTS, an abbreviation of the medical terms for the two conditions.

    Since the FDA granted emergency use authorization (EUA) for the Johnson & Johnson vaccine in late February 2021, nearly 18 million doses of the one-dose vaccine have been given. A total of 60 cases of TTS, including nine deaths, were reported in people who received the Johnson & Johnson vaccine through March 18, 2022. TTS has been seen in men and women across age ranges, but the highest risk was seen in women ages 30 to 49 years.

    The Johnson & Johnson COVID-19 vaccine will still be available in the US to people who cannot or do not want to get an mRNA vaccine. The vaccine’s label and fact sheet has been updated with a warning statement and updated information about authorized use of the vaccine.

    In July 2021 the FDA added another warning to the vaccine’s fact sheet regarding a very small but increased risk of Guillain-Barré syndrome (GBS) following vaccination. GBS is a disorder in which the body destroys its own nerve cells. It can lead to muscle weakness and sometimes paralysis, trouble breathing, or, rarely, death. The revised fact sheet lists symptoms of GBS and urges anyone who experiences them after vaccination to seek immediate medical attention. Once again, the benefits of vaccination outweigh the small increased risk.

    A report published in MMWR found that among US adults without immunocompromising conditions, vaccine effectiveness against COVID-19 hospitalization from March through August 2021, when the Dela variant was circulating but before the Omicron variant was identified in the US, was 71% for the Johnson & Johnson vaccine. This was lower than vaccine effectiveness against hospitalization for the Moderna mRNA vaccine (93%) or the Pfizer/BioNTech mRNA vaccine (88%).

    Vaccine side effects include mild to moderate pain at the site of injection; headache, fatigue, and muscle aches; swollen lymph nodes; unusual feeling in the skin or decreased feeling or sensitivity in the skin; persistent ringing in the ears, called tinnitus; and diarrhea and vomiting.

    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.

    The Johnson & Johnson vaccine can be safely refrigerated for months and frozen for even longer.

    Why did the FDA limit use of Johnson & Johnson’s vaccine?

    In May 2022, the FDA limited use of Johnson & Johnson’s COVID-19 vaccine to adults who cannot get, or refuse to get, one of the mRNA vaccines. The FDA made the decision because of concerns about a rare, but potentially fatal, blood-clotting disorder.

    The blood clots in question involve blood vessels in the brain, lungs, abdomen, and legs, and are accompanied by low levels of blood platelets. This combination is referred to as thrombosis and thrombocytopenia syndrome, or TTS, an abbreviation of the medical terms for the two conditions.

    Since the FDA granted emergency use authorization (EUA) for the Johnson & Johnson vaccine in late February 2021, nearly 18 million doses of the one-dose vaccine have been given. A total of 60 cases of TTS, including nine deaths, were reported in people who received the Johnson & Johnson vaccine through March 18, 2022. TTS has been seen in men and women across age ranges, but the highest risk was seen in women ages 30 to 49 years.

    The Johnson & Johnson COVID-19 vaccine will still be available in the US to people who cannot or do not want to get an mRNA vaccine. The vaccine’s label and fact sheet has been updated with a warning statement and updated information about authorized use of the vaccine.

    While the risk of experiencing a blood clot after vaccination is very low, anyone who experiences the following symptoms after receiving the Johnson & Johnson vaccine should seek immediate medical care:

    • severe or persistent headache
    • chest pain
    • blurred vision
    • severe pain in your abdomen
    • leg swelling
    • shortness of breath
    • tiny red spots under the skin
    • new or easy bruising.

    What needed to happen before the FDA authorized or approved a vaccine for COVID-19?

    Approval of the Pfizer/BioNTech and Moderna vaccines and authorization of Johnson & Johnson's vaccine required 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.

    Safety data continue to be collected and monitored even after the vaccines are approved or authorized.

    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.

    The two mRNA vaccines available in the US are made by Pfizer and BioNTech and Moderna.

    Could an mRNA vaccine change my DNA?

    An mRNA vaccine 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.

    The two mRNA vaccines available in the US are made by Pfizer/BioNTech and Moderna. Both have been granted full approval by the FDA.

    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. If you had an allergic reaction within the first 30 minutes after receiving the first vaccine dose, ask your doctor whether or not you should get a second dose. There are different types of allergic reactions and the specifics of your reaction can help inform the decision.

    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 a severe 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, talk to your doctor about the risks and benefits of getting an mRNA vaccines.

    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. The FDA has granted full approval to the Pfizer/BioNTech (for people 16 years and older) and Moderna (for people 18 years and older) COVID-19 mRNA vaccines. The transition from emergency use authorization (EUA) status to full licensure was based on additional data and longer follow-up showing that the vaccines met certain safety, effectiveness, and manufacturing quality standards.

    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.

    Should I get the COVID-19 vaccine if I already had COVID-19?

    Both COVID infection and full vaccination protect against subsequent COVID infection for several months. A report published in MMWR even suggested that prior infection may be more protective than vaccination. (Data for this study was collected between May and November 2021, before Omicron became predominant, so it may not apply to this variant.) Still, the CDC recommends vaccination for everyone who is eligible, even those who were previously infected. If you are sick with COVID-19, you can get vaccinated as soon as you meet the criteria for discontinuing your isolation.

    I am pregnant and plan to eventually breastfeed my baby. Is it safe for me to get a COVID-19 vaccine?

    The CDC recommends that women who are pregnant, thinking about becoming pregnant, or were recently pregnant — including those who are breastfeeding — should get vaccinated against COVID-19. The American College of Obstetrics and Gynecology (ACOG) and the Society for Maternal-Fetal Medicine also agree that all pregnant and breastfeeding individuals should be vaccinated.

    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, COVID-19 increases risk for premature birth, stillbirth, and possibly also for other undesirable pregnancy outcomes. Results from a large, observational study from Scotland conducted between December 2020 and October 2021 showed that risks to both mother and baby are substantially higher in pregnant women who are unvaccinated, compared to those who are vaccinated.

    Evidence supporting the safety of COVID vaccines for pregnant women and their babies continues to grow. One study published in MMWR looked at data from more than 40,000 pregnant women between December 2020 and July 2021. About 10,000 of these women received a COVID-19 vaccine (typically an mRNA vaccine, either Pfizer/BioNTech or Moderna) during their pregnancy, most during their second or third trimester. Women who were vaccinated against COVID-19 while pregnant were no more likely than unvaccinated women to give birth prematurely or have a baby that was small for its gestational age.

    A study published in NEJM in October 2021 analyzed safety data collected by the CDC. The researchers looked at data from nearly 2,500 women who received a COVID-19 vaccine, either before becoming pregnant or during their first 20 weeks of pregnancy, and found that they did not have an increased risk of miscarriage. A previous study, conducted by the CDC and published in NEJM, found the COVID-19 vaccines to be safe when given during the second or third trimester.

    Increasing evidence shows that vaccine-generated antibodies pass from mother to baby and protect newborns for several months after birth. A small study published in the American Journal of Obstetrics and Gynecology 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. A study published in JAMA found that 98% of babies born to mothers who received an mRNA COVID-19 vaccine during pregnancy had detectable levels of antibodies two months after birth, and 57% of babies had detectable antibody levels six months after birth. And a report published in MMWR found that babies born to mothers who received two doses of an mRNA COVID-19 vaccine during pregnancy were 61% less likely to be hospitalized with COVID in their first six months of life than babies born to mothers who were not vaccinated while pregnant. Protective antibodies are particularly important for infants because COVID vaccines are not authorized for babies younger than 6 months.

    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 cannot reach or cross the placenta.

    Similar to any decision regarding over-the-counter medications and supplements during pregnancy, your own doctor is in the best position to advise you based on your personal health risks and preferences.

    I have been hearing about heart problems in kids and young adults following the COVID vaccine. Should I still get my child vaccinated?

    There has a been a higher-than-expected number of heart inflammation cases after vaccination with the mRNA COVID-19 vaccines, particularly among boys and young men. However, the CDC still strongly recommends that all children 5 years and older be vaccinated.

    As of July 12, 2021, 1,047 reports of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the outer lining of the heart) had been reported in people under age 30, particularly in male teens and young adults, after vaccination with the Pfizer/BioNTech or Moderna mRNA vaccines The CDC’s Advisory Committee on Immunization Practices (ACIP) has said available data "suggest likely association of myocarditis with mRNA vaccination in adolescents and young adults." Even with the increased risk, heart inflammation is a rare occurrence.

    Myocarditis and pericarditis after vaccination was most common in males ages 16 to 24. Cases tended to occur within several days after the second mRNA vaccine dose. Most people who developed myocarditis or pericarditis had mild cases and recovered completely after treatment.

    If your child develops any of the following symptoms within a week of vaccination, seek medical care:

    • chest pain
    • shortness of breath
    • feeling like your heart is beating fast, fluttering, or pounding.

    This or any other potential significant side effect of a vaccine is always of special concern in children. While the risk of COVID causing severe illness and hospitalization is much lower compared to adults, it’s important to remember that at least 1,231 children ages 0 to 18 years have died from COVID. In addition, long-term adverse health effects even after mild infection in children are now being recognized.

    The CDC recommends that all children ages 5 years and older get vaccinated and boosted.

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    Visit our Coronavirus Resource Center for more information on coronavirus and COVID-19.

    Image: Mongkolchon Akesin/Getty Images

    Disclaimer:

    As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles.

    No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.

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