Emerging data from Israel suggests that the Pfizer-BioNTech vaccine's protection against severe Covid-19 and hospitalization wanes over time, but that booster shots dramatically reduced both infections and serious illnesses.

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What the data from Israel revealed

For the study, which was published in the New England Journal of Medicine on Wednesday, researchers looked at data on more than one million individuals in Israel between July 30 and August 22—shortly after the country began offering booster doses to those over the age of 60.

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They found that, among people who had received a booster dose at least 12 days earlier, the rates of new infection were 11 times lower than among people who hadn't received a booster. The rate of severe Covid-19 was almost 20 times lower.

However, the researchers acknowledged the data showed only a short-term benefit to booster doses. "We cannot tell at this point what will happen in the long run," Micha Mandel, a professor of statistics and data science at the Hebrew University of Jerusalem, said.

Additionally, FDA on Wednesday released data that Pfizer had submitted to the agency, also collected in Israel.

It showed that, in absence of booster shots, the efficacy of Pfizer-BioNTech's vaccine drops by about 6% every two months after the second dose is administered. According to Pfizer, that drop is "due to waning of vaccine immune responses" rather than the delta variant.

A booster dose, however, restored protection against infection to 95%. The data was collected from July 1 to Aug. 30, when the delta variant was prevalent in Israel.

In an FDA staff report on Wednesday, the agency's staff advised caution in interpreting data from other countries.

"While observational studies can enable understanding of real-world effectiveness, there are known and unknown biases that can affect their reliability," FDA regulators wrote in the report. Studies done in the United States "may most accurately represent vaccine effectiveness in the U.S. population," they added.

Ultimately, the FDA staff report declined to take a position on whether the agency should approve booster shots. FDA's vaccine advisory committee is scheduled to meet Friday, Sept. 17, to discuss Pfizer's application.

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Health experts remain divided on the use of boosters

According to the Financial Times, 10 countries—including Israel, the United States, the UK, and France—have either announced plans for or have already begun administering booster doses to certain parts of their population.

Even so, health experts remain divided on the decision, as some argue that any available doses would be better used to vaccinate people in less developed countries.

For example, World Health Organization Director-General Tedros Adhanom Ghebreyesus last week called for a moratorium on booster doses through the end of the year, in the hopes of that every country can vaccinate at least 40% of its population.

In addition, a group of 18 vaccine experts—including two departing FDA scientists—on Monday published an article in The Lancet arguing that available doses of coronavirus vaccines should be used to reach currently unvaccinated individuals, rather than for booster shots.

However, National Institute of Allergy and Infectious Diseases Director Anthony Fauci on Wednesday argued that the United States can provide booster shots without sacrificing vaccine doses for people in other parts of the world.

"You can do both," Fauci said. "The way we're doing in this country, you can have a program to give booster, in this case third shots for people who've gotten the two-dose Moderna and Pfizer vaccine, you can get them boosted if you put a considerable amount of resources and effort into getting low and middle income people vaccinated. And that's exactly what we're doing."

Fauci also underscored the strength of data—both in Israel and the United States—indicating that vaccine immunity is waning to support the use of boosters. "If you look at the data, the data [is] strongly suggestive in this country, and more than just suggestive in Israel, that you have a waning of immunity among people across age groups, not just the very very elderly, you have clearly waning of immunity against infection and clear cut indication of waning of immunity against severe disease," he said.

But Marion Pepper, an immunologist at the University of Washington in Seattle, noted that Israel's data showed only that booster shots can improve vaccine protection for a few weeks.

"What I would predict will happen is that the immune response to that booster will go up, and then it will contract again," Pepper said. "But is that three- to four-month window what we're trying to accomplish?" (Banco, Politico, 9/14; Knutson, Axios, 9/13; Sullivan, The Hill, 9/14; Cookson et al., Financial Times, 9/14; Weixel, The Hill, 9/14; Mendez/Lovelace, CNBC, 9/15; Lovelace, CNBC, 9/15; Garfinkel, Axios, 9/15; Knutson, Axios, 9/15; Walker, MedPage Today, 9/15; Hopkins/Schwartz, Wall Street Journal, 9/15; Mandavilli, New York Times, 9/15; LaFraniere/Weiland, New York Times, 9/15; Weiland/LaFraniere, New York Times, 9/15)