Washington, D.C.—A key FDA advisory committee will meet early next month to discuss the need for and timing of additional booster vaccines against COVID-19, as well as whether vaccines need to be updated to respond to specific variants.

The Vaccines and Related Biological Products Advisory Committee will meet virtually on April 6, according to the FDA. Other agencies, including the CDC and the National Institutes of Health, will participate in the meeting.

"As we prepare for future needs to address COVID-19, prevention in the form of vaccines remains our best defense against the disease and any potentially severe consequences," explained Peter Marks, MD, PhD, director of the FDA Center for Biologics Evaluation and Research. "Now is the time to discuss the need for future boosters as we aim to move forward safely, with COVID-19 becoming a virus like others such as influenza that we prepare for, protect against, and treat. Bringing together our panel of expert scientific external advisors in an open, transparent discussion about booster vaccination is an important step to gain insight, input and expert advice as we begin to formulate the best regulatory strategy to address COVID-19 and virus variants going forward."

Part of the impetus for the meeting—which will involve no voting—is that both Modern and Pfizer-BioNTech are seeking FDA emergency use authorization for a fourth booster dose for some people.

Moderna submitted an amended application to include its Spikvax COVID-19 vaccine for a fourth booster dose for people aged 18 years and older who have received an initial booster of any of the authorized or approved COVID-19 vaccines.

Pfizer, Inc. and BioNTech SE are seeking authorization for an additional booster dose for adults aged 65 years and older who have received an initial booster of any of the authorized or approved COVID-19 vaccines.

"The submission is based on two real-world data sets from Israel analyzed at a time when the Omicron variant was widely circulating," the companies wrote in a press release. "These data showed evidence that an additional mRNA booster increases immunogenicity and lowers rates of confirmed infections and severe illness."

Correspondence in the New England Journal of Medicine discussed an open-label, nonrandomized clinical stud in Israel where researchers assessed the immunogenicity and safety of a fourth dose of either BNT162b2 (Pfizer–BioNTech) or mRNA-1273 (Moderna) administered 4 months after the third dose in a series of three BNT162b2 doses. The participants consisted of 1,050 healthcare workers.

"After the fourth dose, both messenger RNA (mRNA) vaccines induced IgG antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptor-binding domain and increased neutralizing antibody titers; each measure was increased by a factor of 9 to 10, to titers that were slightly higher than those achieved after the third dose, with no significant difference between the two vaccines," researchers reported, adding that the fourth dose did not lead to "substantial" adverse events–just the mild systemic and local symptoms seen with other COVID-19 vaccines.

On the other hand, the study pointed out, "A comparison of the initial response to the fourth dose with the peak response to a third dose did not show substantial differences in humoral response or in levels of omicron-specific neutralizing antibodies. Along with previous data showing the superiority of a third dose to a second dose, our results suggest that maximal immunogenicity of mRNA vaccines is achieved after three doses and that antibody levels can be restored by a fourth dose."

The Israeli researchers also observed low vaccine efficacy against infections in healthcare workers, as well as relatively high viral loads, which suggested that those who were infected were also infectious. "Thus, a fourth vaccination of healthy young healthcare workers may have only marginal benefits," they explained. "Older and vulnerable populations were not assessed."

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