A Guide to COVID-19 Vaccine Booster Shots

There’s been quite a bit of news about COVID-19 booster shots lately, and it’s been more confusing than reassuring. Public health officials don’t agree on whether everyone needs a booster yet, and in the same way that the vaccines were rolled out to different groups of people one category at a time as government agencies reviewed studies to make sure they were safe and effective, boosters are being doled out to certain people first. Here’s where we stand for now.

If the vaccines work, why do I need a booster?

The three vaccines that are currently available in the U.S.—from Pfizer-BioNTech, Moderna and Johnson&Johnson-Janssen—are still highly effective in protecting you from getting COVID-19 disease. They are slightly less effective in protecting you from getting infected with the virus in the first place, but people who are vaccinated still have a five times lower rate of infection with SARS-CoV-2 than people who aren’t vaccinated, and a more than 10-fold rate of hospitalizations and deaths from the Delta variant of the virus.

Several months after getting the vaccine, the level of antibodies against the COVID-19 virus starts to wane, so public health officials feel that it makes sense to boost those numbers back up with another dose of the shot. There is some evidence that with each additional shot, the body starts making higher quality antibodies that are better at recognizing and blocking new variants of the virus, including Delta.

Who is eligible for a booster shot right now?

In August, the U.S. Food and Drug Administration (FDA) and Centers for Disease Control (CDC) authorized booster shots for anyone who has been vaccinated with either Pfizer-BioNTech or Moderna shots against COVID-19 and has a compromised immune system due to, for example, chronic illnesses, transplant surgery or cancer treatment, among others.

As of September 2021, that recommendation expanded to include certain people who received the Pfizer-BioNTech vaccine. The FDA and CDC now recommend that people who were originally vaccinated with two doses of the Pfizer-BioNTech shot should get a booster six months after their last dose if:

The FDA and CDC also included others who initially got the Pfizer-BioNTech vaccine, but said the booster wasn’t mandatory for them. The following people can get a booster if they want to:

These decisions came after the FDA and CDC reviewed studies from Pfizer-BioNTech on the safety and efficacy of a booster dose among a broader group of people who received the approved two doses of the shot, and then got another dose at least six months later. The agencies also looked at data from Israel, where some people have been getting booster doses since July 30.

Taken together, these data showed that after several months, levels of virus-fighting antibodies start to drop—though they also showed that people are still protected from getting severe COVID-19 disease and getting hospitalized. Still, the waning immunity worries public health officials, especially since the Delta variant, which spreads more quickly, is now the dominant version of the virus behind new infections around the world. In a study of a several hundred people who received a booster dose, researchers from Pfizer-BioNTech reported that the additional dose is safe and can raise antibody levels back up to those achieved immediately after the second dose, particularly among people over age 65 years. Israeli health officials also reported that older individuals who got a booster dose were 11 times less likely to get infected with SARS-CoV-2, and 19.5 times less likely to get severe COVID-19 than those receiving only two doses.

If I’ve been vaccinated with Moderna or Johnson&Johnson-Janssen, can I get a booster?

At the moment, no. The FDA and CDC have only reviewed the safety and efficacy of boosters using the Pfizer-BioNTech vaccine. Moderna has submitted its data to the FDA to review, and the agency is expected to make a recommendation in coming weeks. Johnson&Johnson-Janssen, which makes the only authorized single-shot COVID-19 vaccine in the U.S., has not yet provided the FDA with data on its booster, although the companies have reported early data showing that a second shot can increase antibody levels by nine-fold in people ages 18 to 55 years compared to after the initial single dose.

Why are decisions about Moderna and Johnson&Johnson-Janssen boosters taking longer?

The timeline for the booster doses is mirroring that of the original vaccines. Pfizer-BioNTech were the first to submit a request to the FDA for authorization of its vaccine. in November 2020; Moderna followed about 10 days later, and J&J filed its request in February 2021. The FDA issued emergency use authorization for all of them, based on two-month follow up data showing that the shots were both safe and efficacious, on a similar timeline, with Pfizer-BioNTech getting authorization first, followed by Moderna and then J&J. (In August 2021, after reviewing longer term data on safety and efficacy that stretched to six months, the FDA fully approved the two-dose regimen of the Pfizer-BioNTech vaccine, making it the first approved COVID-19 shot. Moderna has also provided longer follow up data to the FDA and is waiting for the agency’s decision about full approval.)

In order to get authorization for a booster, each of the vaccine manufacturers had to conduct additional studies on the safety and efficacy of an additional dose, and then follow the people in those studies for several months to document any side effects as well as effects on immunity.

Is the Pfizer-BioNTech booster a different vaccine from the original one?

No, the booster shot of the Pfizer-BioNTech vaccine is the same dose, and the same vaccine used in the first two doses.

Will the Moderna booster follow Pfizer-BioNTech’s model and be another dose of the same Moderna vaccine?

It’s not clear yet, as Moderna is testing different versions of a booster. The company is testing a booster that is half the dose of the original two doses, one that is the same dose, another that is a different vaccine that targets the Beta variant, and finally one that combines the original and Beta variant boosters in a single shot. Moderna and the FDA will decide, based on the results of those studies, which booster will help the most people to stay protected against COVID-19.

I’ve heard that people who received Moderna or Johnson&Johnson-Janssen are getting booster shots.

This may be possible, but health officials say it’s not recommended. Researchers are still studying how people react to mixing doses from different vaccine manufacturers, so it’s not clear yet whether that’s a safe thing to do. And just as importantly, there are no data showing that getting a booster of a different vaccine will continue to protect you from COVID-19.

Will I have to provide proof that I was originally vaccinated with the Pfizer-BioNTech shot in order to get a booster?

Technically, yes, but CDC director Dr. Rochelle Walensky said that the CDC is urging vaccine providers not to deny people shots, so vaccinators likely would not be asking for documentation, opting instead to ask people to self-attest that they are eligible. However, vaccination sites will have different policies to verify eligibility. Walgreens, for example, says they will ask people to attest that they meet the requirements for a booster when they schedule their appointment, and again just before they get their shot, but pharmacists won’t require documentation. “Ultimately we are focused on removing barriers and improving access to vaccines,” a spokesperson tells TIME.

According to a spokesperson for the UCLA Medical Center, if patients have been treated at that hospital, doctors can check their electronic health records to learn which vaccine they received. For people who aren’t patients there, health providers are asking them to bring their vaccination card to verify that they originally received the Pfizer-BioNTech shot.

And for those who misplaced their card, providers are likely asking people to self-attest that they received the Pfizer-BioNTech shot, and that it’s been at least six months since their last dose. In general, sites probably won’t be asking for proof that you meet the age, underlying health condition, or occupational risk criteria.

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