WASHINGTON — A panel of independent experts advising the Food and Drug Administration will recommend Tuesday whether existing Covid-19 vaccines should be updated to address a newer version of the coronavirus in a booster shot that Americans will receive in the fall could get.
The federal government hopes to improve the vaccine to better boost people’s immunity before the virus is likely to resurface this winter. But to do that quickly, it may have to forgo the lengthy human trials that have been used over the past two years to test coronavirus vaccines in favor of a faster process that relies more on lab and animal testing.
The most recent trials on human volunteers have lasted five months, even with relatively small groups. But the virus is evolving so quickly that new vaccine formulations are already obsolete before such trials are even completed.
Pfizer and Moderna, the two major vaccine manufacturers, have both studied an updated vaccine targeting the Omicron variant, which became dominant last winter. Both companies took a financial risk and started producing doses, hoping the government would pick it out as the fall booster.
But Omicron itself has been overtaken by a succession of sub-variants that began nearly three months ago, and many scientists argue it’s a bygone threat.
“Omicron is clear in the rearview mirror,” says Dr. Peter J. Hotez, a vaccine expert at Baylor College of Medicine. A booster targeting Omicron makes no sense, he said, unless it also works against the latest sub-variants, adding, “I haven’t seen any evidence of that.”
At a meeting on Tuesday, the FDA will ask the advisory panel whether a redesigned vaccine should target a version of the virus in the Omicron family. That would leave it to federal regulators to decide exactly which formulation to use in the fall.
Scientists initially had high hopes for a so-called bivalent vaccine that would combine the existing formulation with a vaccine targeting Omicron itself. Clinical trial results released this month by Moderna and Pfizer, with its partner BioNTech, showed that it induced higher levels of antibodies to Omicron than existing vaccines.
But while the companies announced the findings, outside scientists were unimpressed by the less than twofold increase. dr. Dan H. Barouch, a virologist at Beth Israel Deaconess Medical Center in Boston who collaborated with Johnson & Johnson and Pfizer on some studies of the coronavirus vaccine, described it as “relatively modest.” And the FDA said in a new briefing paper to the advisory committee that bivalent targeting of Omicron is “already somewhat outdated.”
Federal health officials may instead push for a bivalent vaccine that would target BA.4 and BA.5, two sub-variants of Omicron. They are now responsible for more than a third of infections in the United States and may be more like the incarnation of the virus that circulates in the fall.
But a bivalent targeting those subvariants would also be problematic. Neither Pfizer nor Moderna has focused on developing it, and no one is sure how well it would work. At this late time of the year, the use of human trials to test such a vaccine, followed by the two months it would take to produce doses, would push the introduction of each new vaccine well into the next wave of the can push the virus.
That suggests officials should base their judgment largely on animal and lab testing.
dr. Kelly L. Moore, president of Immunize.org, a nonprofit dedicated to increasing vaccination coverage, said such an accelerated process has already been used to update the flu vaccine every year.
While this is the country’s first attempt at using the next generation of Covid vaccines, she said, existing ones have been safely given to hundreds of millions of people. Updating them may take “very educated guesswork,” she said, but such deductions are “appropriate for the circumstances.”
If the government eventually goes for a booster shot targeting BA.4 and BA.5, it will still be a race to produce the doses in the fall, even with accelerated testing. According to two people familiar with the company’s operations, Pfizer may be able to meet the October deadline.
But dr. Paul Burton, Moderna’s medical director, said in an interview last week that the company is unlikely to be able to deliver doses until very late this year or even early next year. “I don’t think we would be in a position to be prepared to support the fall booster campaign,” he said.
There is also a chance that the virus could re-evolve and render the updated vaccine ineffective.
“Do we make it to BA.4 and 5? They will likely peak sometime in the next two months,” said Dr. John Beigel, director of clinical research at the National Institutes of Health, who has conducted multiple studies on coronavirus vaccines. “They may be old news by the time fall comes.”
dr. Beigel said one option was to just stick with the existing vaccines, which continued to provide robust protection against serious illness but very little against infection.
The Centers for Disease Control and Prevention estimated that by February, 60 percent of Americans had already been infected with the virus, giving them at least some temporary immunity. Although breakthrough infections among vaccinated individuals are now common, many of the cases are mild.
Still, the World Health Organization said this month that updated versions of the vaccines should be studied because of the rapid deterioration in protection against symptomatic diseases.
dr. Beigel and other public health officials say the virus is increasingly nimble at evading the antibodies that are the first line of defense against infection. Studies show that the existing booster injections generate a significantly lower level of neutralizing antibodies against BA.4 and BA.5 than against Omicron.
On average, 290 Americans die from Covid every day and nearly 4,400 are hospitalized each day, according to the Centers for Disease Control and Prevention. The FDA briefing document said the risk of another major Covid outbreak would increase later this year “due to the combination of declining immunity, further evolution of variants and increased indoor activity.”
The advisory panel is likely to split between those who think a fall booster will be broadly necessary and those who want to limit extra shots to high-risk individuals. dr. Arnold Monto, a professor of public health at the University of Michigan and chair of the panel, predicted that a large portion of the population would receive booster shots.
“We know there is a decline,” he said in an interview. “We need to boost, and it’s better to boost with something more relevant” than the existing vaccines.
On the other side is Dr. Paul A. Offit, a vaccine expert at the Children’s Hospital in Philadelphia. “The number of hospital admissions has fallen. The number of deaths is much lower because we are protected from serious diseases,” he said. “That is what counts.”
He said only people over 70 and over 50 with serious underlying conditions are likely to need a booster shot, as Covid infections can have serious consequences in those groups.
How much the government has to spend can ultimately determine the size of a new booster campaign. Congress turned down a White House request for $22.5 billion in emergency funds for coronavirus, and a compromise plan to spend $10 billion has stalled since April. The government has shifted $5 billion in funds for coronavirus testing and protective equipment to buy new vaccines.
“With the resources we’ve been able to gather to collect vaccines for the fall together, it’s very clear that we won’t have enough vaccines for every adult who wants one,” Dr. Ashish K. Jha, the White House Coordinator for the Pandemic Response, said at a briefing last week.