CDC Director Endorses Pfizer, Moderna Boosters for All US Adults

Brenda Goodman

November 19, 2021

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Centers for Disease Control and Prevention (CDC) Director Rochelle Walensky, MD, signed off on a recommendation Friday evening to let all US adults get a COVID-19 booster shot.

The endorsement, following a unanimous vote by a panel of CDC advisors earlier in the day backing a third dose of a Moderna or Pfizer mRNA COVID vaccine, now means everyone over the age of 18 is eligible for a booster.

“After critical scientific evaluation, today’s unanimous decision carefully considered the current state of the pandemic, the latest vaccine effectiveness data over time, and review of safety data from people who have already received a COVID-19 primary vaccine series and booster.

"Booster shots have demonstrated the ability to safely increase people’s protection against infection and severe outcomes and are an important public health tool to strengthen our defenses against the virus as we enter the winter holidays. Based on the compelling evidence, all adults over 18 should now have equitable access to a COVID-19 booster dose,” Walensky said in a prepared statement.

Earlier Friday the US Food and Drug Administration (FDA) authorized boosters for both the Pfizer and Moderna vaccines for all adults, setting the stage for the CDC's decision.

The Advisory Committee on Immunization Practices, or ACIP, recommended that the additional dose be given at least 6 months after the second dose.

They also strengthened a recommendation that everyone over the age of 50 should get a third dose of, whether or not they have an underlying health condition that may increase their risk from a COVID-19 infection.

The committee voted 11 to 0 to in favor of both policies.

Reassuring Safety Information

The panel based its decision on the results of a new study of boosters in Pfizer vaccine recipients, as well as reassuring safety information that’s being collected through the CDC and the FDA's monitoring systems.

Pfizer presented the early results from a study of 10,000 people who had all received two doses of its vaccine. Half of the study participants received a third shot, or booster. The other half got a placebo.

The study is ongoing, but so far, six of the people in the booster group have gotten a COVID-19 infection with symptoms compared to 123 people who got COVID-19 in the placebo group, making boosters 95% effective at keeping people from getting sick.

Most people in the study had gotten their original doses about 10 months earlier. They’ve been followed for about 10 weeks since their booster.

Importantly, there were no study participants hospitalized for COVID-19 infections in either the placebo or booster group, indicating that the first two doses were still very effective at preventing severe outcomes from infection.

In the Pfizer study, the benefits of boosters were seen as fast as 7 days after study participants got their shots.

The majority of side effects after a third Pfizer dose were mild and temporary. Side effects like sore arms, swelling, fever, headache, and fatigue were more common in the booster group — affecting about 1 in 4 people who got a third shot.

Vaccination side effects were less common after boosters than have been seen after the second dose of the vaccine, with one exception: swollen lymph nodes, which were more common after boosters, but were temporary.

Some cases of myocarditis and pericarditis have been reported after people received vaccine boosters, but the risk for this heart inflammation appears to be extremely low, about two cases for every million doses given.

There were 54 cases of myocarditis reported so far to the Vaccine Adverse Event Reporting System, or VAERS. To date, only 12 have met the case definition and are considered related to vaccination. Most of the reported cases are still being studied.

The risk of myocarditis after a booster dose may be less likely than it is after receipt of second vaccine doses, but it’s still too early to be sure said the CDC’s Tom Shimabukuro, MD, MPH, who leads the vaccine safety study team.

There was less data on how well third shots are working for Moderna vaccine recipients. The company presented very little new data on its half-dose boosters. But based on blood tests, it seems that their boosters also substantially increase antibody levels.

In addition to preventing symptomatic infections, there’s new evidence that booster doses may stop transmission of the virus, at least for a couple of months. 

Sara Oliver, MD, who is an officer with the the CDC’s Epidemic Intelligence Service, highlighted two recent studies showing that boosters provide protection against asymptomatic infections, which could help curtail the spread of the virus.  

Boosters may help stop even asymptomatic infections because they boost a person’s antibodies to a level that provides so-called sterilizing immunity.

The Infectious Diseases Society of America (IDSA) supported Friday's decisions, imploring all eligible Americans to take action.

"As cases are rising in some parts of the United States, infectious diseases experts urge everyone who is eligible — including children 5 and older — to get vaccinated. Before you travel or gather with loved ones this holiday season, get vaccinated so you can celebrate safely," IDSA President Daniel P. McQuillen, MD, said in a prepared statement.


CDC, Advisory Committee on Immunization Practices, Webcast, Nov. 19, 2021.


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