Demand for booster doses of COVID-19 vaccines is likely to rise now that the Food and Drug Administration (FDA) has expanded eligibility to all adults and in light of concerns about the new Omicron variant. The latest clinical data supports the safety and efficacy of boosters in adults, as well as vaccination in younger children. Even so, the science on dosing regimens and safety continues to evolve, said Peter Marks, MD, PhD, director of FDA Center for Biologics Evaluation and Research and acting director of FDA Office of Vaccines Research and Review.
In an AMA webinar recorded prior to the emergence of the Omicron variant, Dr. Marks ran through the latest data and recommendations on booster shot regimens, and the evidence supporting the recent authorization of the Pfizer pediatric vaccine for 5–11-year-olds.
This is the ninth episode in AMA’s “COVID-19: What Physicians Need to Know” webinar series. Each installment gives doctors fact-based insights from the nation’s highest-ranking subject-matter experts working to protect the public health during the COVID-19 pandemic.
Making sure doctors have access to that information is essential given the vital part physicians play in helping people make decisions about COVID-19 vaccination.
“As an immunologist, I can tell you that physicians play an important role as vaccine ambassadors for our patients,” said Susan R. Bailey, MD, the AMA’s immediate past president and the webinar’s moderator.
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Boosters demonstrate restorative effects
People vaccinated 10 months ago may not have sufficient immunity to protect against the highly virulent Delta variant, said Dr. Marks. An additional vaccine dose may offer more durable immunity, preventing hospitalizations and deaths and possibly the symptoms of long COVID.
The FDA last month authorized the use of booster shots for the Moderna and Pfizer-BioNTech mRNA vaccines in all adults 18 or older, expanding eligibility beyond seniors and high-risk adults.
A Pfizer study of booster shots in 10,000 people, 11 months after they were first vaccinated, found that boosting restored immunity (relative to vaccine efficacy) to about 95%.
“We’re hoping as these individuals are followed for a longer period that maybe we’ll see more durable immunity than after the first two doses,” Dr. Marks said.
Vaccine confidence will drop if too many breakthrough infections occur with these boosters, he said. This underscores the importance of setting the right schedule for these shots.
“Ultimately, the primary series for COVID-19 or its successor will be a regimen separated by more months,” Dr. Marks said.
Federal regulators have given the green light to mix and match booster shots. However, “we won’t know for a long time what the most optimal combination is,” said Dr. Marks.
Side effects minimal in younger kids
Dr. Marks also compared the latest Pfizer data for 5–11-year-olds with data on older children and young adults. To date, Pfizer is the only vaccine authorized for use in children and adolescents in the U.S.
Clinical trials in 5–11-year-olds had the distinction of taking place during the Delta variant surge. The child clinical trial participants also got a smaller dose than other cohorts: 10 micrograms, or one-third of an adult dose.
Data on 4,600 children 5–11 showed that the vaccine was more than 90% effective against the Delta variant. The younger children treated with the 10-microgram dose also had a better profile in terms of fatigue and flu-like symptoms, though still had some injection-site pain.
The FDA is closely monitoring cardiac side effects seen in teenage males, said Dr. Marks. Such events have generally been mild, associated with one-day hospital stays and anti-inflammatory remedies.
Interactions between the vaccine and androgenic steroids may be leading to some inflammatory-mediated events in young men, he said. There’s optimism that younger children won’t have the same myocarditis risks seen in teenagers.
What’s coming for kids under 5
Emergency use authorization for vaccines in children under 5 is highly anticipated. But you can’t rush the science, noted Dr. Marks.
“One needs to further dose de-escalate as one goes below age 5,” he said. “We want to make sure we get the safety right and we want to make sure the benefits-and-risks considerations are right.”
Various companies working through trials are expected to come to the FDA in early 2022 with data. “We’ll work very rapidly to evaluate this data with the same care as the other authorizations,” Dr. Marks said.
