In a daylong virtual meeting, a panel of experts advising the Food and Drug Administration came out in general support of efforts to develop new COVID-19 vaccines tailored to variants.
The committee wasn't asked to vote on any specific recommendations to the agency but instead discussed the framework for making decisions about when to change the viral strain or strains used for future vaccines, including boosters.
"I think we're in uncharted territory because with SARS-CoV-2 a lot of things have happened that have never happened before," said Dr. Arnold Monto, professor emeritus at the University of Michigan and acting chair of the committee.
It's likely the panel will reconvene in May or June to consider a more specific proposal for reformulation of COVID-19 vaccines.
The process used to tweak annual flu vaccines to match circulating strains is one model that may inform the process for COVID-19, but there are still many unknowns about how the coronavirus may change and stark differences between the influenza virus and SARS-CoV-2.
Fall target for new kind of booster
The critical consideration is whether a variant-specific booster should be made available this fall. The rise of the omicron variant, and lately a subvariant called BA.2, has sharpened the question. The vaccines now in use in the U.S. are based on the form of the virus that circulated at the beginning of the pandemic and are less effective against some later strains.
"Although we've seen a major decline in the number of COVID-19 cases in the country, the virus continues to circulate and it will continue to do so and will potentially cause waves of an increased numbers of cases," said Dr. Peter Marks, head of the FDA's Center for Biologics Evaluation and Research, at the start of the meeting. "This is of particularly concern as we head into the fall and winter season."
Marks also noted that the coronavirus will have had another more time to evolve by the time fall arrives in the U.S.
During the morning session, Israeli researchers presented data on the waning protection of a single booster dose of the Pfizer-BioNTech vaccine and the increased protection of a second booster against infections, which was fleeting, and severe illness, which was longer lasting. The rapid spread of the omicron variant contributed to the decline in protection from immunization with one booster.
Israeli authorities approved a second booster in early January for people 60 and older and others at high risk or who worked in health care. The Israeli experience contributed to the FDA's decision in late March to authorize a second booster dose for people 50 and older as well as for other people with compromised immune systems.
Predicting viral evolution is 'quite difficult'
Rapid genetic changes in the coronavirus are driving its ability to evade the immune response from vaccination and prior infections. The continuing changes complicate decisions about which strains to include in new vaccines.
"In general, from everything we've seen, we should expect a lot of evolution going forward, and we should have methods to keep up with this evolution in terms of our vaccination platforms," said Trevor Bedford, who studies viral evolution at the Fred Hutchinson Cancer Center in Seattle.
He said that predicting where the virus is headed is "quite difficult." The coronavirus has been evolving must faster than the flu. Significant new variants of the coronavirus have emerged in just months instead of the years it can takes for the flu to make such jumps.
Based on the rate of the coronavirus' evolution so far and uncertainty about what lies ahead, Bedford estimates a dangerous new variant like omicron could emerge within about a year and a half or maybe not for more than a decade.
There isn't much time to make vaccine changes in time for an immunization push this fall. "If you're not on your way to a clinical trial by the beginning of May, I think it's going to be very difficult to have enough product across manufacturers to meet demand," said Robert Johnson, deputy assistant secretary of the federal Biomedical Advanced Research and Development Authority.
FDA's Marks acknowledged that there is a compressed timetable for deciding upon booster makeup, but there may be "some wiggle room" that could allow for a determination in May or June.
There's a lot riding on the decision. "We simply can't be boosting people as frequently as we are," Marks said, adding that the second booster dose authorized recently by FDA was "a stopgap measure" to help protect the most vulnerable people.
The goal for a reformulated booster sometime later this year, Marks said, would be to "boost again in order to protect against a wave that could come at the time we're at highest risk."
In closing remarks, committee chair Monto said, "We'd love to see an annual vaccination similar to influenza but realize that the evolution of the virus will dictate how we'll respond."
Rob Stein contributed to this report.
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