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Pfizer says booster shot is needed, but not because of Delta

Meantime, the FDA’s staff declined to take a stance on a third shot, in advance of a Friday meeting of outside advisors, and Moderna reported new data on breakthrough infections.

A syringe is prepared with Pfizer's COVID-19 vaccine.
A syringe is prepared with Pfizer's COVID-19 vaccine.Matt Rourke/Associated Press

As a federal advisory panel prepares to meet Friday on a request by Pfizer to clear a COVID-19 booster shot, the drug giant is arguing that although its messenger RNA vaccine is highly effective against the Delta variant, recipients will need a third dose because protection against all strains wanes over time.

In a 53-page analysis released Wednesday by the US Food and Drug Administration, Pfizer strives to thread a needle. It contends that people need a booster about six months after the second shot not because of the surge in infections driven by the highly contagious Delta variant, but because the effectiveness of its vaccine decreases after six to eight months.


”Evidence is building to suggest that administration of booster doses of COVID-19 mRNA vaccines is potentially an urgent emerging public health issue,” said the company, which developed the first vaccine rolled out in the United States with its German business partner, BioNTech.

The FDA’s staff declined to take a position on boosters in another document posted online Wednesday, saying that regulators haven’t verified all the available data. But the agency said that all three coronavirus vaccines ― used to fully vaccinate more than 179 million Americans ―still protect them from severe disease and death caused by the virus.

Two days before an independent panel of scientific advisers to the FDA meet, the agency also released a Pfizer analysis that said the declining performance of its two-shot vaccine is “likely primarily due to waning effectiveness” in general “rather than due to Delta escaping vaccine protection.” Pfizer cited a study by the Kaiser Permanente Southern California health care system suggesting that two doses initially was more than 90 percent effective against the variant.

Overall, data from Pfizer’s late-stage trial of about 44,000 volunteers ― undertaken before Delta emerged ― indicated that two shots provided 96.2 percent protection for up to two months, 90.1 percent protection for up to four months, and 83.7 percent after four months.


The company is also citing the experience of Israel, the first country to fully vaccinate a majority of its citizens against COVID-19. Data from Israel’s recent rollout of a third shot of Pfizer’s vaccine restored waning protection levels to 95 percent effectiveness, the firm said. The booster also raised no significant new safety concerns, Pfizer said, although a fever was more common as a side effect following a third dose than after the first two.

In contrast to the overwhelming support that Pfizer’s two-dose vaccine received when the 15-member panel ― officially called the Vaccines and Related Biological Products Advisory Committee ― cleared it for emergency use on Dec. 11, the request for a booster shot for individuals 16 and older is expected to get a more skeptical reception Friday.

One committee member, Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, recently said he believes mRNA vaccines made by Pfizer and Cambridge-based Moderna will probably turn out to be three-shot regimens. But, he said, a third dose of either vaccine is unnecessary now for most people, and that the federal government should concentrate on vaccinating the millions of Americans who have yet to get shots.

Another committee member, Dr. H. Cody Meissner, director of Pediatric Infectious Disease at Tufts Medical Center, said this week he hasn’t made up his mind how he will vote and needs to review briefing documents.


Nonetheless, he said he has yet to see compelling data that any of the three coronavirus vaccines cleared for use ― including a third vaccine from Johnson & Johnson that uses different technology ― lose the robust protection they provide against severe illnesses that cause hospitalization or death.

“The point that seems to consistently get lost in all of this is that a booster shot is not going to end the pandemic,” Meissner said. “What’s going to end the pandemic is to get every single person who refuses to get the vaccine vaccinated.”

Pfizer itself acknowledged in its analysis that “unvaccinated individuals continue to account for most SARS-CoV-2 infections and severe cases.”

A group of international experts, including two outgoing FDA vaccine regulators, argued in a paper published Monday in the Lancet that approving booster shots now would be premature.

The paper was co-written by Marion Gruber and Phil Krause, veteran FDA officials who have been spearheading the agency’s review of COVID-19 vaccine applications. The authors said that “widespread boosting should be undertaken only if there is clear evidence that it is appropriate.” If an unnecessary rollout led to significant side effects, they added, it could undermine the acceptance of many vaccines, not just those for COVID-19.

The participation of Gruber and Krause in the paper represented an unmistakable rebuke to President Biden’s administration, which on Aug. 18 announced plans for booster shots to start the week of Sept. 20. That announcement appeared to anger some federal health regulators who felt the president got ahead of the scientific community, which had not reached on a consensus on boosters.


The situation has set the stage for a potentially awkward meeting Friday, in part because Gruber is listed as one of the first speakers scheduled to start the discussion. The other scheduled speakers at the daylong virtual meeting include Dr. Sharon Elroy-Preis, head of public health at Israel’s Health Ministry.

Some medical experts who have been following Pfizer’s request for a booster shot say it’s possible that the FDA advisory panel will recommend the agency approve a third dose, but only for a limited group of people who might be particularly vulnerable, such as those over the age of 65.

On Aug. 13, the FDA authorized certain people who got two doses of Pfizer or Moderna vaccines to receive an additional dose if they had compromised immune systems, including some organ transplant recipients and cancer patients.

The FDA doesn’t have to follow the recommendation of its advisory committee, but usually does. If the agency does endorse booster shots, an advisory panel to the US Centers for Disease Control and Prevention is expected to vote soon afterward on who should get them and when.

Moderna has also applied to the FDA for approval of a booster dose, although it is not as far along in the process. On Wednesday, the company announced the results of a study that detected 162 breakthrough infections among 14,746 people who received their first Moderna shot a median of 13 months previously, compared with 88 breakthrough infections among 11,431 people who received their first Moderna shot a median of eight months previously. Moderna said the data indicated waning immunity that could be boosted with a third shot.


Jonathan Saltzman can be reached at jonathan.saltzman@globe.com.