FDA Neutral on Moderna Bid for COVID Booster Ahead of Decisive Meeting

Brenda Goodman, MA

October 12, 2021

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

The US Food and Drug Administration (FDA) is keeping its cards close to the vest when it comes to the potential approval of a booster dose of Moderna's COVID-19 vaccine, now called Spikevax.

In a briefing document posted ahead of a Thursday meeting of its Vaccines and Related Biological Products Advisory Committee, the agency acknowledged that real-world data present a mixed picture when it comes to the need for boosters.

"Some real world effectiveness studies have suggested declining efficacy of Moderna COVID-19 Vaccine over time against symptomatic infection or against the Delta variant, while others have not," the agency writes. "However, overall, data indicate that currently US-licensed or authorized COVID-19 vaccines still afford protection against severe COVID-19 disease and death in the United States."

The agency noted that factors that would support the authorization of a booster include:

  • The effectiveness of the primary series — doses 1 and 2 — over time and against circulating variants

  • The effectiveness of the booster in preventing important outcomes, including infection, hospitalization, and death; and how that effectiveness holds up over time

  • The dynamics of the pandemic in the United States

  • The risks of the booster

Half Dose

There are some surprises in the briefing document too.

On September 3, Moderna had originally applied for an Emergency Use Authorization (EUA) for a booster for everyone over the age of 12.

Because the Spikevax primary series is not yet authorized for children and teens ages 12 to 18, and after Pfizer's bid to give boosters to teens failed, the company revised its EUA.

Moderna is now asking the FDA to approve a 50-mg booster, which is half the dose of the original shots, for everyone over the age of 65, and for those ages 18 to 64 who are at greater risk for COVID because of an underlying health condition or who are exposed to the virus frequently at work. 

This is the same population considered for Pfizer boosters.

The most commonly reported adverse events after the Moderna booster were mild, and included fatigue, muscle and joint pain, swelling at the injection site, headache, and chills. 

People ages 18 to 64 were more likely to report these reactions compared with individuals 65 and older. There were no serious adverse events reported within 28 days after the booster in a small study.

A data analysis of COVID-19 infections occurring in people who participated in Moderna's original vaccine study suggests that immunity against infection waned over time and in the wake of the Delta variant. 

Among 15,200 study participants who were on average about 13 months past their second dose of the vaccine, the rate of COVID-19 infections was 77 cases per 1000 person-years.

The rate, however, was lower, at 49 cases for every 1000 person-years, in study participants who got the placebo first and were vaccinated later, making them about 8 months past their last dose.

The FDA cautioned, however, that it has not independently verified the company's data.

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