We can predict how well the vaccine will be working
In the ongoing effort to stay ahead of a virus that continues to evolve, Pfizer and BioNTech have offered the first human evidence that their updated bivalent COVID boosters produce a meaningfully stronger immune response against the Omicron variants now circulating. The data arrives after the shots were already authorized and distributed — a sequence that reflects a broader tension in modern public health between the urgency of protection and the patience required by science. What emerges is not a story of failure or triumph, but of institutions navigating uncertainty in real time, with incomplete maps and genuine stakes.
- Updated bivalent boosters targeting BA.4 and BA.5 showed substantially higher neutralizing antibodies in adults over 55 compared to the original vaccine formulation.
- The shots were already authorized and distributed in September — before any human trial data existed — a decision that drew unease from some scientific advisers who wanted clinical evidence first.
- Regulators defended the early rollout by drawing a parallel to annual flu vaccine updates, which are approved on mechanistic and animal data rather than new human trials each season.
- Critical data on adults aged 18 to 55 remains incomplete, leaving a gap in the full picture of how broadly the updated booster performs across age groups.
- The FDA is now weighing whether to convene advisers on updating the primary vaccine series itself — a potentially larger shift that will hinge on accumulating human clinical evidence.
Pfizer and BioNTech released the first human trial results this week on the updated COVID boosters that have been in circulation since September. The new shots are bivalent — combining a component targeting the original coronavirus strain with one aimed specifically at the BA.4 and BA.5 Omicron subvariants. Blood samples drawn from 80 participants a week after vaccination showed a substantial increase in neutralizing antibodies against those variants. Among adults over 55, the contrast with the original booster was especially pronounced.
The safety profile appeared essentially unchanged from prior formulations. Pfizer CEO Albert Bourla called the findings a validation of the company's approach, expressing optimism that the updated shots could help curb winter surges. But the data has limits: the trial results released so far cover only participants over 55, and BioNTech confirmed that comparisons in the 18-to-55 age group are still underway.
The announcement carries an unusual context. The FDA and CDC authorized these boosters in September based on mouse studies and prior variant data — before human trials were complete. Some advisory panel members were uncomfortable with that sequence, but regulators concluded that waiting months for full trial results posed greater risks than moving forward. FDA vaccine chief Peter Marks compared the approach to how flu vaccines are updated annually — through mechanistic understanding and animal data rather than new human studies each year.
Looking ahead, the FDA may convene advisers to consider whether the primary vaccine series should also be updated to the new formulation — a broader decision that will depend on further clinical evidence. For now, the bivalent boosters remain authorized only for those who have already completed their initial vaccination.
Pfizer and BioNTech released the first human trial data this week on the updated COVID boosters that have been rolling out across the country since September, and the results suggest the new shots will work better against the Omicron variants now circulating than the original vaccine formulation did.
The updated boosters are "bivalent"—a term that means they contain two components working in tandem. One targets the original coronavirus strain. The other is designed specifically to protect against BA.4 and BA.5, the Omicron subvariants that have dominated infections in recent months. The companies examined blood samples from 80 people who received the new boosters, drawing samples a week after vaccination. Across the board, recipients showed what the companies described as a substantial increase in neutralizing antibodies against BA.4 and BA.5. When researchers looked specifically at people older than 55, the contrast became clearer: those who had received the original booster showed a more limited antibody response to these variants compared to those who got the updated version.
The safety profile of the new boosters appeared essentially identical to the original shots, the companies said. Pfizer CEO Albert Bourla framed the findings as validation of the company's approach. "These early data suggest that our bivalent vaccine is anticipated to provide better protection against currently circulating variants than the original vaccine and potentially help to curb future surges in cases this winter," he said in a statement.
But the data released so far is incomplete. The trial included only people over 55. Alexander Siebert, a BioNTech spokesperson, acknowledged that comparisons in younger adults aged 18 to 55 are still underway. "These are the first data coming out of the trial and currently only a comparison in the above 55 age group was completed to the original vaccine. We don't have data yet on the 18-55 year old adults," he said. Moderna, which also developed an updated booster, did not respond to requests about when their human trial data would be available.
The timing of this announcement is worth understanding. The FDA and CDC authorized the updated boosters in September, before any human trial data existed. The decision rested on mouse studies conducted by Pfizer and Moderna, as well as historical data from previous variant-targeted vaccines that had been tested in humans. Some CDC advisers expressed discomfort with approving the shots without human clinical evidence first. But the agencies and a majority of the advisory panel concluded that the benefits of rolling out the boosters immediately outweighed the risks of waiting months for full trials to complete. Peter Marks, the FDA's vaccine chief, compared the decision to how influenza vaccines are handled each year—strain changes are approved based on mechanistic understanding and animal data, not new human trials. "We know from the way the vaccine works and from the data that we have that we can predict how well the vaccine will be working," he told reporters.
The FDA indicated it may convene its own advisory panel later this year to discuss whether the primary series vaccines—the initial shots given to people who have never been vaccinated—should also be switched to the updated formulation. That decision will likely depend on accumulating more human clinical data, the agency said. For now, the bivalent boosters are authorized only for people who have already completed their primary vaccination series.
Citas Notables
These early data suggest that our bivalent vaccine is anticipated to provide better protection against currently circulating variants than the original vaccine and potentially help to curb future surges in cases this winter.— Pfizer CEO Albert Bourla
We know from the way the vaccine works and from the data that we have that we can predict how well the vaccine will be working.— FDA vaccine chief Peter Marks
La Conversación del Hearth Otra perspectiva de la historia
Why did the FDA approve these boosters in September if they didn't have human data yet?
They had mouse data and historical precedent. The agencies decided that waiting months for full trials while BA.4 and BA.5 were already spreading widely posed its own risk—people would be unprotected. It's a calculation, not a certainty.
But some CDC advisers wanted to wait. What was their concern?
They wanted to see human evidence first before rolling out something new to millions of people. It's the more cautious position. The majority disagreed, but it wasn't unanimous.
So this new data—does it settle the question?
It answers part of it. For people over 55, yes, the updated booster clearly produces more antibodies against BA.4 and BA.5. But we still don't know how younger adults respond. And antibodies are a proxy for protection, not protection itself.
What happens next?
They finish the younger age group data. The FDA probably convenes advisers again. And they decide whether to switch the primary series vaccines to this new formulation. That's the bigger question—not just boosters, but the baseline shot everyone gets.
And Moderna?
Still waiting on their human data. They did mouse studies too, but they haven't released clinical trial results yet.