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Israeli officials say Pfizer vaccine less effective as Delta variant spreads

Experts say getting vaccinated will protect you from the Delta variant.Lane Turner/Globe Staff

With the Delta variant spreading through Israel, officials there say they are seeing a decline in the effectiveness of the Pfizer coronavirus vaccine, though it remains highly effective at preventing serious illness.

The Israeli Ministry of Health said that an epidemiological analysis had found that since June 6 there was a “marked decline in the efficacy of the Pfizer vaccine in preventing infection (64%) and symptomatic illness (64%).”

“This decline has been observed simultaneously with the spread of the Delta variant in Israel,” the ministry said in a statement.

At the same time, “The vaccine maintains an efficacy rate of about 93% in preventing serious illness and hospitalization cases,” the officials emphasized.


Ministry officials had published a report in May that two doses of Pfizer’s vaccine provided more than 95 percent protection against infection, hospitalization, and severe illness, Reuters reported.

Israel, a world leader in vaccinations, emerged from lockdown in the spring. But recent case increases have resulted in the reinstatement of mask requirements for indoor gatherings and public transportation. And the government is considering more restrictions.

Professor Nadav Davidovitch, who sits on the government’s expert advisory committee on the coronavirus, told the Financial Times the new finding was based on “preliminary” figures gathered by health authorities. “Delta is a lot more infectious, but appears to not lead to as much serious illness and death, especially given that we now have the vaccine,” he said.

The Pfizer two-dose vaccine is the most-administered in the United States, with 183.3 million doses administered, compared with 135 million for the two-dose Moderna vaccine, and 12.6 million for the one-dose Johnson & Johnson vaccine, according to the Centers for Disease Control and Prevention. And the Delta variant is on the rise here. Officials have cited the danger of the variant as they have urged people to get their shots.


Andy Slavitt, formerly a senior adviser to President Biden’s pandemic response team, said in a series of tweets that the news is “worth paying attention to” because it could affect when Americans need to get booster shots.

He said the data was “very preliminary” and “could be an outlier. But if the data hold, the most likely conclusion is not that Delta is escaping the vaccine . . . Instead it’s possible that this is a signal that immunity could simply be waning in certain populations. Recall that Israelis vaccinated before the US. So our first sign of a vaccine waning will likely be seen in Israel.”

“People who take from this there is no point in getting vaccinated because they aren’t perfect are quickly running the exact wrong direction,” he said. “The US is prepared. Deaths & hospitalizations are preventable with vaccinations even if or when they wane . . . Not getting vaccinated is the real risk. Every day it becomes even clearer.”

Some experts were cautious about the Israeli finding.

Ran Balicer, chief of the professional coronavirus cabinet which advises Israel’s coronavirus cabinet, told the Israeli newspaper Haaretz that there were “enormous methodological challenges in properly assessing the efficacy of the vaccine from local outbreaks.” He told the Times of Israel that it was “too early to precisely assess vaccine effectiveness against the variant.”

Dr. Ashish Jha, dean of the Brown University School of Public Health, tweeted that, in speaking to colleagues in Israel, he had found “real skepticism about [the] 64% number.”


He said the finding “may turn out to be right,” but the “best data still suggest” mRNA vaccines like the Pfizer and Moderna vaccines offer a “high degree” of protection against infection and “superb protection” against severe illness.

The “bulk of evidence says vaccines work very well against Delta,” he said.

Martin Finucane can be reached at