The two companies cited initial data from a clinical trial that showed a booster dose given six months after the second dose had a consistent tolerability profile while still creating high immune responses against the Wuhan wildtype strain and the Beta (South African) variant. Those immune titers were five to 10 times higher than those observed after the two primary doses.
Also, data from a study published in Nature showed that in laboratory tests, the immune cell levels observed shortly after the second dose of the primary two-dose shots had strong neutralization titers against the Delta variant (originating in India). They expect a third dose would boost the titers even higher, just as it did for the Beta variant. Studies are continuing.
They point out that real-world data released from the Israel Ministry of Health demonstrated that vaccine efficacy for both preventing infection and symptomatic disease had dropped six months after vaccination, even though the vaccine’s ability to prevent serious illness was still very high.
“These findings are consistent with an ongoing analysis from the Companies’ Phase III study,” they stated. “That is why we have said, and we continue to believe that it is likely, based on the totality of the data we have to date, that a third dose may be needed within six to 12 months after full vaccination.”
However, on July 8, the U.S. Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) issued a statement saying, “Americans who have been fully vaccinated do not need a booster shot at this time.” Along with the National Institutes of Health (NIH), they indicated they are researching “whether or when a booster might be necessary.”
The statement said, “The United States is fortunate to have highly effective vaccines that are widely available for those aged 12 and up. People who are fully vaccinated are protected from severe disease and death, including from the variants currently circulating in the country, such as Delta. People who are not vaccinated remain at risk. Virtually all COVID-19 hospitalizations and deaths are among those who are unvaccinated.”
The Pfizer-BioNTech vaccine is predominant in many parts of the world. In the European Union, the Pfizer-Vaccine accounts for two-thirds of doses, and in Israel, it is the only vaccine used. In the U.S., it makes up more than half of COVID-19 vaccinations.
Some experts are skeptical about the need for a booster, even in light of the more contagious Delta variant. The Delta variant is believed to be approximately 60% more contagious than the Alpha variant, which originated in the UK, estimated to be twice as contagious as the Wuhan wildtype variant. And there are questions about Pfizer and BioNTech’s seeming conflict of interest on the subject, given their financial benefit from a third dose.
Celine Gounder, an infectious disease specialist at Bellevue Hospital Center in New York, told The New York Times, “There’s really no indication for a third booster or a third dose of an mRNA vaccine, given the variant that we have circulating at this time. In fact, many of us question whether you will ever need boosters.”
Although the Israel study appears solid, other studies are indicating the Pfizer-BioNtech vaccine is still highly effective at preventing infection against all variants.
“Pfizer looks opportunistic by hanging an announcement on the back of very early and undigested data from Israel,” John Moore, a virologist at Weill Cornell Medicine in New York, told The New York Times. “When the time is right for using boosters here, the decision isn’t theirs to make.”
Another issue is whether discussing the need for boosters in the U.S. is appropriate when there are still billions worldwide who have yet to receive a single dose.
“It’s impossible to ignore the global situation,” said Natalie Dean, a biostatistician at Emory University in Atlanta. “It’s hard for me to imagine getting a third dose when there are frontline workers treating Covid patients who still haven’t been vaccinated.”
And Gounder points out that unvaccinated people are the source of potential new variants. “If we’re worried about variants, our best protection is to get the rest of the world vaccinated, not to hoard more doses to give third doses of mRNA vaccines to people here in the U.S.”