On Wednesday, a panel of vaccine advisers
to the Food and Drug Administration spent hours debating key questions for
revamping the shots and conducting future booster campaigns. They didn’t reach
any firm conclusions.
The questions facing the experts included:
How often to update the vaccines against new strains, how effective they should
be to warrant approval and whether updates should be coordinated with global
health authorities.
Last week, the FDA authorized a fourth dose
of the Pfizer or Moderna vaccines for anyone 50 or older and for some younger
people with severely weakened immune systems. It’s an effort to get ahead of
another possible surge.
But the FDA’s vaccine chief Dr. Peter Marks
acknowledged at the meeting “we simply can’t be boosting people as frequently
as we are.” He called the latest booster update a “stopgap” measure to protect
vulnerable Americans while regulators decide whether and how to tweak the
current vaccines.
Marks cautioned that waning vaccine
protection, new variants and colder weather in the fall could raise the risk of
more surges.
“Our goal here is to stay ahead of future
variants and outbreaks and ensure we do our best to reduce the toll of disease
and death due to COVID-19,” said Marks, adding that he expects more meetings of
the vaccine panel in coming months.
Some of the key questions the panel
discussed:
HOW SHOULD THE U.S. DECIDE WHEN TO LAUNCH
FUTURE ROUNDS OF BOOSTER SHOTS?
One area where experts appeared to agree is
that vaccines should be judged on their ability to prevent severe disease that
leads to hospitalization and death.
“We need to focus on the worst case, which
is severe disease, and we need to change strains when we’re losing that
battle,” said Dr. Mark Sawyer of the University of California, San Diego.
By that measure, the current vaccines have
held up remarkably well.
During the last omicron-driven surge, two
vaccine doses were nearly 80% effective against needing a breathing machine or
death — and a booster pushed that protection to 94%, federal scientists
recently reported.
But only about half of Americans eligible
for a third shot have gotten one. And many experts said it was unsustainable to
continue asking Americans to get boosted every few months.
A panelist from the Centers for Disease
Control and Prevention suggested that the 80% protection from severe disease
could become the standard for evaluating the vaccines.
“I think we may have to accept that level
of protection and then use other alternative ways to protect individuals with
therapeutics and other measures,” said Dr. Amanda Cohn, CDC’s chief medical officer.
Presentations at the meeting by government
health officials and independent researchers underscored the challenges of
predicting when the next major COVID-19 variant might appear.
Trevor Bedford, a disease modeler with the
Fred Hutchinson Cancer Research Center, said a major new strain like omicron
could emerge anywhere from every 1.5 years to once a decade, based on currently
available data. Given that unpredictability, researchers will need methods to
quickly determine whether current vaccines work against emerging variants.
WHAT’S THE PROCESS FOR UPDATING VACCINES TO
ADDRESS NEW VARIANTS?
All three COVID-19 vaccines now used in the
U.S. are based on the original coronavirus version that emerged in late 2019.
Updating the vaccines will be a complex task, likely requiring coordination
between the FDA, manufacturers and global health authorities.
To speed the vaccines to market, the FDA
relied on research shortcuts to judge effectiveness, mainly looking at their
early impact on the immune system’s antibody levels. A number of panelists said
Wednesday they wanted more rigorous data from studies that track patients over
time to see who gets sick or dies.
But that approach would likely be too time
consuming.
“We’re looking at a conundrum here in that
it’s going to be hard to generate all the data we want in short order when a
new variant emerges,” said Dr. Ofer Levy of Harvard Medical School.
A representative for the U.S. Biomedical
Advanced Research and Development Authority laid out the narrow window that
manufacturers could face to reformulate, study and mass produce an updated
vaccine by September.
“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 BARDA.
The process for updating annual flu
vaccines offers one possible model, as laid out by a representative from the
World Health Organization.
Twice a year, WHO experts recommend updates
to flu vaccines to target emerging strains. The FDA then brings those
recommendations to its own vaccine panel, which votes on whether they make
sense for the U.S., setting the stage for manufacturers to tweak their shots
and begin mass production.
But COVID-19 hasn’t yet fallen into a
predictable pattern like the flu. And as the coronavirus evolves, different
strains may become dominant in different regions of the world.
Several experts said they would need more
meetings with more data and proposals from the FDA to decide on a strategy.
“We’ve never been here before. We’re all
working together to do the best we can and it’s very complex,” said Oveta
Fuller of the University of Michigan’s Medical School.