Frequently Asked Questions

On August 23, the U.S. Food and Drug Administration granted full approval to the Pfizer-BioNTech COVID-19 vaccine for individuals 16 and older. To date, two other COVID-19 vaccines, one produced by Moderna and another by Johnson & Johnson, have received FDA emergency approval in the United States.  The Pfizer vaccine is also available to children 12 to 15 years old under emergency use authorization. While all of these vaccines were shown to be safe and effective through clinical trials, it’s natural to have questions about them.

You can check this page for updates and science-based answers to frequently asked vaccine questions.

How do I know the COVID-19 vaccines are safe?

All approved COVID-19 vaccines (Johnson & Johnson, Moderna, Pfizer) went through all the required stages of clinical testing needed to prove two things: that they’re safe and work to protect against COVID-19.

Real-world data backs this up. Over 382 million vaccine doses were administered in the United States so far and more than 5.8 billion doses have been administered around the world. Very few serious reactions have been reported.

Four conditions have occurred in vaccinated people. Some individuals developed anaphylaxis (a strong allergic reaction). Others developed myocarditis (inflammation of the heart muscle). Some people who received the Johnson & Johnson vaccine have reported a certain type of blood clot called thrombosis with thrombocytopenia syndrome (TTS) or Guillain Barré Syndrome, a condition in which the immune system attacks the nerves. Of the millions of people who were vaccinated, only a handful have developed any of these conditions.

Out of every one million vaccinated people between two and five people went into anaphylaxis. The CDC is still monitoring cases of myocarditis (you can find the latest numbers here), but fewer than 1,000 cases have been confirmed. Of the 14 million J&J vaccines administered, 45 developed these blood clots as of September 1, 2021. And, there are only 185 reports of Guillain Barré in the CDC’s vaccine safety monitoring system as of September 1 (the CDC regularly updates numbers here).

The risk of experiencing these complications is extremely low. Meanwhile, there are serious risks associated with COVID-19, including severe illness or hospitalization.

The CDC takes safety very seriously and continues to monitor these vaccines calling the effort “the most intense safety monitoring” in U.S. history.

Do vaccines protect people in the real world?

Yes! For instance, in Israel, scientists examined the real-world vaccine effectiveness of the Pfizer vaccine by comparing 596,918 vaccinated people to unvaccinated controls. After the second dose, the vaccine was 92 percent effective in preventing COVID-19 and 87 percent effective in preventing hospitalizations.

There are other studies in the U.S. and Scotland that all speak to the effectiveness of these vaccines in the real world.

Scientists are still studying how long this immunity lasts and how variants, like the Delta variant, may affect it. There is evidence the vaccines can protect against the Delta variant. For example, one CDC study analyzed the vaccine’s ability to prevent visits to the emergency room, or urgent care clinics in nine states, between June and August 2021. The study found that all three approved vaccines were 86 percent effective in preventing hospitalization.

This study was conducted as the Delta variant became dominant, and suggests the vaccine is still protective in the face of its spread. It’s also the largest U.S.-based real-world study of vaccine effectiveness to date.

Will I need a booster shot if I am already vaccinated?

On August 12, the FDA approved a third dose of Pfizer or Moderna vaccines for a subset of immunocompromised people. Specifically, people who received solid organ transplants, or have a condition that leaves immune systems similarly compromised.

On August 18, U.S. public health officials and medical experts announced the recommendation of a booster shot to maximize protection and prolong the durability of the vaccine based on the data available to date. The data showed that protection against SARS-CoV-2 infections decreases over time after the initial doses of vaccination. There was also evidence of reduced protection against mild or moderate disease. Booster shots will be provided as the protection against severe disease, hospitalization and death could diminish in the upcoming months, especially for high-risk groups.

In a September 17 meeting, an advisory panel to the FDA recommended boosters for people 65 and older and people 16 and over who are at high risk of getting severe COVID-19 or who work in settings that make them more likely to get infected, such as health care workers, emergency responders and teachers. The panel did not extend the recommendation to any other groups. The FDA is not required to follow the recommendations of its advisory committees, but it generally does. The FDA is expected to announce more guidance on booster shots soon.

What about the variants? Does the vaccine protect against them too?

Research is still ongoing into how vaccines fare against certain variants, but there are signs that they still offer protection.

Protection Against Delta

The Delta variant now makes up 93 percent of COVID-19 cases in the U.S, per NYU Langone. Vaccines are still effective in preventing severe disease and death from the Delta variant.

Real-world data backs this up. An August CDC study on healthcare workers found that vaccine efficacy declined from 91 to 66 percent as Delta surged, but this is still a very high level of protection. Even more recent research, published in September suggests protection is even higher than that, though.

All three vaccines were 86 percent effective in preventing hospitalizations. However, protection for older people was slightly lower. The vaccines were 76 percent effective for people 75 and older. This is still a very high level of protection, suggesting that in the face of Delta, these vaccines still work.

A new CDC study looking at COVID-19 cases, hospitalizations and deaths in 13 states between April and July showed that unvaccinated people were 10 times more likely to be hospitalized for COVID-19 and 11 times more likely to die of it than people who got the vaccine. This is strong evidence showing that, even in the face of Delta, the vaccines are doing their job.

Protection Against Lambda

The World Health Organization currently designates Lambda as a “variant of interest,” but it is not yet designated as a “variant of concern.” In short, scientists are keeping an eye on it.

There have been fewer than 1,000 Lambda cases detected in the US, as of September 13. The primary variant of concern at the moment is the Delta variant.

A pre-print (not peer-reviewed) study suggests antibodies produced by Pfizer and Moderna vaccines, and to a lesser extent, J&J, could neutralize the Lambda variant.

Protection Against Mu

As of September, the Mu variant is also listed as a variant of interest according to the World Health Organization. But it is not yet classified as a variant of concern.

The CDC has not listed Mu as a variant of interest yet. In September Anthony Fauci, the Director of the National Institute of Allergy and Infectious Diseases said the agency was paying attention to Mu, but it is not considered an immediate threat.

Should I get a vaccine if I’ve already had COVID-19?

The short answer is yes.

While you may have COVID-19 antibodies (proteins that bind to the virus and tell the body to vanquish it) in your body after you recover, we don’t know how long immunity gained from natural infection lasts.

By contrast, scientists know that the COVID-19 vaccines also give your body a dose of those antibodies, as well as stimulate other types of immune system protections that may lead to more robust protection.

There’s one more reason to get vaccinated: You can help protect others. One study on 365,000 households in England, for instance, found that when some family members were vaccinated, they were half as likely to pass the original coronavirus to an unvaccinated (and vulnerable) person.

The Delta variant is even more contagious than the original coronavirus, which means that vaccinated people can also spread that version of the virus. However, the vaccine will still protect you from getting very sick from Delta. Reducing the chances of getting very sick can also help others by keeping the hospitals from becoming overwhelmed.

If I already got one Pfizer/Moderna shot, why do I need to get the second one?

Real-world research has shown that immunity is improved after two shots. For instance, the effectiveness of one Pfizer or Moderna vaccine against the original coronavirus was 64 percent in a study of U.S. healthcare workers done by the CDC. But two shots raised the efficacy to around 94 percent in that study.

In light of new variants such as Delta and Lambda, it’s even more important to get both doses of your COVID-19 shot.

For example, a Public Health England September report shows that one dose of a vaccine is just 35 percent effective against the Delta variant. Whereas, two doses of the vaccines were 79 percent effective against the Delta variant.

Should I get the vaccine if I’m pregnant or want to become pregnant?

You should talk to your doctor if you are pregnant and are worried about getting a COVID-19 vaccine. However, the CDC now strongly recommends pregnant people (or those who want to become pregnant) get the COVID-19 vaccine.

One study published in the New England Journal of Medicine followed over 35,000 pregnant women who got vaccinated. The study found no signs that the vaccine was linked to any complications. A pre-print study released in August shows that mRNA vaccines were also not linked to any increased risk of miscarriage.

Meanwhile, evidence also shows that pregnant women who get COVID-19 are at higher risk of getting very sick from the virus itself compared to non-pregnant women of the same age. This means protecting against the virus with a vaccine is even more important.

Does the vaccine affect fertility?

You may have heard some misinformation recently suggesting that the vaccines might impair a woman’s ability to get pregnant. Scientists have debunked this claim.

In a joint statement, the American Society for Reproductive Medicine, the American College of Obstetricians and Gynecologists, and the Society for Maternal-Fetal Medicine said there is no evidence the vaccine impacts women’s fertility. The idea that there could be fertility loss due to vaccination was “scientifically unlikely,” the statement read.

For men, a study done at the University of Miami found no evidence that men who got Pfizer or Moderna vaccines had any irregularities in their sperm as a result of vaccination.

The Mayo Clinic also notes that there is “no evidence” that COVID-19 vaccines can cause fertility problems.

How safe is the vaccine for children?

The CDC currently recommends that children aged 12 years or older get the Pfizer vaccine. There is no approved vaccine yet for kids younger than 12. These recommendations were made after studies specifically evaluated the safety of this vaccine in children and the data was reviewed by outside experts.

For example, a clinical trial on 2,260 adolescents aged 12 to 15 found no serious adverse effects linked to the vaccine. Meanwhile, the vaccine was 100 percent effective in protecting against COVID-19.

A CDC study released in August 2021 analyzed data from two CDC programs evaluating the safety of vaccines in children. Of the 8.9 million adolescents vaccinated during the study period, there were 9,246 adverse event reports, of which 90 percent were not serious. The most common serious event listed was myocarditis, noted in 397 cases.

Myocarditis is more common in adolescent males aged 12-29, per CDC research. However, myocarditis is also a complication of COVID-19, the disease the vaccine can prevent in the first place. A CDC study released in August found that children under 16 who got COVID-19 have 37 times the risk of developing myocarditis than those who did not get the virus. The vaccine available for children over 12 will protect against COVID-19 infections.

You might have heard of terms like “breakthrough infections” or have noted some places have reinstated mask mandates.

While these changes can seem scary, the bottom line is vaccines are still the best tool we have to protect ourselves and our families from COVID-19. Masks are an additional tool to help protect people who haven’t yet been vaccinated or lower the chances of spreading the virus to another person.

Even in a world with safe and effective vaccines, public health researchers are constantly researching SARS-CoV-2 and other coronavirus variants. This work will inform the other safety precautions we may need to take, which means that guidelines can change as scientists learn more. Here is what we know so far about breakthrough infections and masks.

What is a breakthrough case?

A “breakthrough case” occurs when a person tests positive for COVID-19 at least 14 days after they have been fully vaccinated. You are deemed fully vaccinated after receiving two doses of Moderna and Pfizer vaccines and one dose of Johnson and Johnson’s vaccine.

You may have noticed an uptick in news coverage about breakthrough cases lately. It isn’t a reason to fear that the vaccines aren’t working. Since so many people are being vaccinated, the CDC expects to see some breakthrough infections occur.

Initial studies of the vaccines indicated that Moderna and Pfizer’s vaccines were about 95 percent effective in preventing disease, and Johnson and Johnson’s were about 66.3 percent effective. Even in these cases, there is some chance that you could get sick after being vaccinated. But your chances of getting sick without a vaccine remain far higher.

Even as we battle the more contagious Delta variant, evidence suggests these vaccines are still protecting most people. One CDC study conducted on about 600,000 COVID-19 cases across 13 states showed unvaccinated people were 4.5 times more likely to get a COVID-19 infection,10 times more likely to be hospitalized, and 11 times more likely to die of COVID-19 compared to vaccinated people.

Even if a breakthrough infection occurs, there is a lower chance of getting extremely ill from it, and the vaccine still protects most people from getting sick at all.

How common are breakthrough cases?

Due to incomplete data, it’s impossible to know for sure how common breakthrough cases are. The CDC doesn’t track breakthrough cases that don’t result in hospitalization or death, as of May 2021.

Right now, data suggests they’re rare.

In July 2021, data collected from 25 states by the Kaiser family foundation showed that breakthrough infections only occurred in less than one percent of vaccinated people in all of those states. The analysis estimates that the rate of breakthrough cases ranged from .1 percent to .29 percent.

Are breakthrough cases dangerous?

The majority of the individuals who got COVID-19 after being fully vaccinated, experienced less severe symptoms, the CDC notes.

Even in the case of the Delta variant, it seems breakthrough cases are rarely severe.

Over 176 million people received vaccines and the CDC reports that more than 15,790 people have been hospitalized and about 2,500 died due to a breakthrough infection. That is a very small fraction of people compared to the millions who have safely received vaccines, and not gotten sick.

Ultimately, the risks of getting very sick from COVID-19 are far higher if you are not vaccinated.

However, it is still important to stay home if you have any symptoms of COVID-19. While the risks of getting very sick are low, if you are infected with the Delta variant, you could risk passing on a case to someone else.

Do I need to wear a mask if I am vaccinated?

As of July 27, 2021, yes. The CDC now recommends fully vaccinated people wear masks indoors if they live in areas of the country where the virus is surging.

It is a reversal from the CDC’s May guidance due to new information about the Delta variant and its transmissibility.

Early-stage studies have shown that people infected with the Delta variant carry far more virus (called “viral load”) than those infected with the original coronavirus. Having a higher viral load doesn’t make people get sicker, but it is a factor that makes it easier to pass the virus to others.

Other preliminary studies, though, suggest viral load declines faster in vaccinated people compared to unvaccinated people, which could impact our ability to continuously spread it.

While vaccines still protect against severe illness, they may not be as effective in preventing someone from passing the Delta variant on to another person. That’s why wearing masks is still important.

Studies show masks can stop us from passing on the coronavirus – one study in Beijing found that masks were 79 percent effective in preventing transmission within a home, for example. Masking in high transmission areas or enclosed spaces can help stop us from spreading the disease to vulnerable people.

Do kids need to wear masks at school this fall?

As of July 27, the CDC recommends both vaccinated and unvaccinated students wear masks when they return to school this fall.

Wearing masks in school helps protect immunocompromised students or students too young to be vaccinated (only about 30 percent of students 12-17 were vaccinated as of July 2021). In light of information on the contagiousness of the Delta variant, masks will also help slow the spread of COVID-19.

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