The U.S. Food and Drug Administration (FDA) has authorized a second booster dose of either mRNA COVID-19 vaccine—Pfizer-BioNTech or Moderna—for older Americans and immunocompromised people. The authorization, which came Tuesday, will make the additional doses available to certain populations that are at a higher risk of severe disease, hospitalization, or death from COVID-19.
The news follows evidence that while a first booster dose can enhance protection against COVID-19, that protection can wane in the four months after vaccination.
"Current evidence suggests some waning protection over time against serious outcomes from COVID-19 in older and immunocompromised individuals," Peter Marks, MD, PhD, director of the FDA's Center for Biologics Evaluation and Research said in a news release Tuesday. "Based on an analysis of emerging data, a second booster dose of either the Pfizer-BioNTech or Moderna COVID-19 vaccine could help increase protection levels for these higher-risk individuals."
The Centers for Disease Control and Prevention (CDC) is expected to issue its own advice on the heels of the FDA's decision, as to who should consider getting the extra dose. The FDA's emergency use authorization (EUA) will allow a second booster dose of either mRNA vaccine for adults over the age of 50 and certain individuals 12 years of age or older (Pfizer-BioNTech) or 18 years of age or older (Moderna) who are immunocompromised at least four months after receiving their first booster dose.
Effectiveness of a Second Booster
There's not a ton of data on the efficacy of fourth doses (or second booster doses) of mRNA vaccines. And according to CNBC, the FDA made this decision to authorize second booster doses without help from its vaccine advisory committee.
But, the FDA news release, along with press releases from both Pfizer and Moderna, shared that the authorization approvals and requests for second booster doses were based in part on real-world data from Israel.
For one preprint study–which is a study that has not yet been peer-reviewed–researchers looked at data from more than 1 million people, age 60 or older and eligible for a fourth dose, collected from the Israeli Ministry of Health database during a time when the Omicron variant was dominant. Highlights of the study's findings included:
- Rates of infection among those who received a second booster dose (technically four doses of a Pfizer-BioNTech vaccine) were two times lower than those who only received a single booster dose.
- Rates of severe illness were four times lower in those who received a second booster.
A second, slightly smaller preliminary study, looked at data from an ongoing, open-label, non-randomized clinical trial among health care workers in Israel who were at least 18 years or older. Out of a group of 700 health care workers, all of whom were previously fully vaccinated and received one booster dose of the Pfizer-BioNTech vaccine, 154 received a second Pfizer booster shot and 120 received their second booster as Moderna. Researchers found that the fourth COVID-19 vaccine dose restored neutralizing antibody levels to those measured at their peak after a third dose.
In the study among health care workers, however, researchers found that a fourth dose of a vaccine wasn't quite as effective in preventing mild or asymptomatic COVID-19 infections, which, according to study authors, means a next generation vaccine (one that is highly protective against future variants) is needed.
"The studies out of Israel show that it [a fourth shot] is a little bit less effective…in preventing us from getting COVID, but it's still very effective in preventing you from getting severely ill from COVID, being hospitalized or dying," Rob Rohatsch, MD, emergency medicine physician and Chief Medical officer at Solv Health, told Health.com. "We're going to have to do our own studies in this country but my anticipation is this is going to be beneficial to perhaps more groups."
Current Booster Dose Recommendations
The FDA's authorization, and the CDC's impending recommendations, for a second booster dose for both mRNA vaccines only applies to people over the age of 50, and certain people over the age of 12 who are immunocompromised. However, the CDC urges all Americans over the age of 12 who have received their primary vaccine series to get a first booster dose. Additionally:
- People who received two Pfizer-BioNtech or Moderna vaccines may receive their first booster dose at least five months after their primary series.
- Those who received the single-dose Johnson & Johnson vaccine may receive a first booster two months after their J&J shot.
In each situation, the CDC recommends people receive an mRNA vaccine as a booster.
This guidance, however, may be changing soon: The FDA's Vaccines and Related Biological Products Advisory Committee is expected to meet on April 6 to discuss the future of COVID-19 booster doses in the U.S. No specific recommendations are expected to be made during this meeting, but the committee is also expected to discuss current and emerging variants, as well as potential vaccine efforts to address them.
Despite the new authorization for a second booster dose, a large portion of the US population has yet to receive their first booster dose: CDC data shows that only about 45% of the total population has received a single booster dose. In that case, it's imperative for everyone in the U.S. to be up to date on their COVID-19 vaccinations. For some, as of today, that may mean a second booster shot; for others, it could mean a first booster or primary series.
The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.
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