A panel of experts advising the U.S. Centers for Disease Control and Prevention just endorsed a plan by the U.S. Food and Drug Administration to offer COVID vaccine booster shots to millions of the most vulnerable Americans.
But the same 15-member panel wanted the CDC to also consider a new vaccine strategy that wasn’t on the agenda for the two-day virtual advisory meeting on Wednesday and Thursday. Several of the panelists urged the CDC to take a hard look at mixing and matching the three different vaccines the FDA has approved for distribution in the United States in a so-called “heterologous” approach that could allow, say, a resident of an assisted-living facility who first got the two-dose Moderna vaccine to later boost their immunity with a single dose of the Pfizer vaccine.
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Or the other way around. A front-line worker who got two Pfizer jabs at first could boost it with a single Moderna jab. Likewise, a recipient of Johnson & Johnson’s single-dose vaccine with an underlying health condition could prolong their own immunity by adding a shot of Pfizer or Moderna.
The advantage is obvious. Mixing and matching vaccines could allow all vulnerable Americans to get boosted, instead of just the roughly half of that group that got the Pfizer vaccine as their “prime” jab. “I have a real problem with the idea the FDA would only want this booster going to people who’ve taken Pfizer,” panelist Sarah Long, a professor of pediatrics at the Drexel University College of Medicine in Pennsylvania, said during the CDC meeting.
Heterologous vaccination is already common in much of the world. It’s high time the U.S. government started coming around to the idea, too, some of the CDC panelists said during their meeting. “Hopefully we can address that very soon,” said panelist Matthew Daley, a senior investigator at Kaiser Permanente’s Institute for Health Research in Colorado.
Outside experts agreed with Daley’s sentiment. Any two or three doses of vaccine should protect against COVID. “From a medical perspective, I don’t think it matters” which jabs are in the mix, Jeffrey Klausner, a former professor of medicine and public health at UCLA, told The Daily Beast.
“I think mixing is long overdue,” Lawrence Gostin, a Georgetown University global-health expert, told The Daily Beast.
But others urged the CDC to take it slow. “My sense is it’s probably fine,” Irwin Redlener, the founding director of Columbia University’s National Center for Disaster Preparedness, told The Daily Beast in reference to heterologous vaccination. “But … it’s a little unclear how or if we should weigh in on this until all data has been examined.”
The two-day CDC panel considered four proposals based on an FDA panel’s own vote last week to endorse a third shot of the Pfizer messenger-RNA vaccine for certain vulnerable Americans who’ve already gotten two doses of Pfizer for their prime vaccination.
The FDA panelists convened amid concerns that vaccine-induced immunity might fade over time or in the face of more aggressive variants of the novel-coronavirus. They voted in favor of boosters for Pfizer-vaccinated Americans 65 years of age and older, as well as for younger Americans ages 16 to 64 who are vaccinated with Pfizer but might be at increased risk of COVID owing to health or work conditions.
The FDA previously authorized boosters for millions of vaccinated Americans with specific immune disorders resulting from disease or organ transplants. The FDA isn’t required by law to act on its panelists’ advice, but it almost always does. To ignore the experts could undermine public confidence in the agency and the drugs it regulates.
The CDC panel slightly narrowed the FDA’s booster plan. By a vote of 15 to zero, the panelists approved a third dose of Pfizer for all Americans 65 and older, six months after prime vaccination. They also endorsed, 13 to two, a booster for Pfizer recipients ages 50 to 64 who have underlying health conditions. The third vote, nine to six in favor, approved a booster for 18-to-49-year-olds with underlying health conditions.
The fourth vote, nine to six against, rejected boosters for Pfizer recipients ages 18 to 64 who might get exposed to COVID at work, including prisoners, residents of homeless shelters and certain front-line workers. The panelists justified the no vote by reminding the CDC’s moderators that younger vaccinated Americans who are in good health are already strongly protected against COVID without a third dose.
There was a fifth vote many of the panelists wanted to take, but which wasn’t on the CDC’s agenda. Nirav Shah, director of the Maine Center for Disease Control and Prevention, urged the public-health agency to consider the “mix and match strategy” as soon as possible. “I recognize we don’t have all the data,” Shah conceded.
It’s not that there’s no data, it’s just less comprehensive than many experts and regulators would prefer. Russia’s Sputnik vaccine, which combines two different vaccine formulations, is in widespread use, but scientists outside of Russia have never been totally happy with the Russian government’s refusal to fully share the data from the vaccine’s large-scale trials.
A small-scale Spanish trial earlier this year studied the efficacy of a single dose of the two-dose vaccine from the AstraZeneca-Oxford consortium followed by a single dose of the two-dose Pfizer vaccine. The mix proved effective, according to experts who reviewed the trial results. But the trial group was too small, young and healthy to produce reliable data, they warned. “The study has limited representativeness.”
The German government briefly championed mix-and-match vaccination this spring after some people reported negative side-effects from their first dose of AstraZeneca. Regulators paused the AstraZeneca vaccine and advised those who’d already gotten their first jab to complete their vaccination with Pfizer or Moderna.
It was advice born of desperation, however, as the first decent study of the mix’s effectiveness didn’t get published until after the German government recommended it. Fortunately for regulators and thousands of everyday Germans, that study found the mix-and-match formula produced antibodies and T-cells at a level “higher or comparable in magnitude to homologous mRNA vaccine regimens.”
In other words, the German mix actually appeared to be better than two doses of Pfizer or Moderna—at least in this one study.
This handful of studies and regulatory recommendations isn’t enough for the CDC. “We are not voting on mix-and-match today,” one agency moderator told the panel on Thursday.
But the same moderator acknowledged the panelist’s eagerness to at least start talking about heterologous vaccination. If and when the FDA acts on the CDC panel’s endorsement and authorizes boosters for millions of Americans—a move that could come within days—it will quickly become obvious that offering boosters only to Pfizer recipients leaves out a lot of vulnerable people. “We’ve heard your voice loud and clear,” the moderator said to advocates of vaccine-mixing.
