According to the Israeli government, a fourth shot of the Pfizer-BioNTech coronavirus vaccine produced a fivefold boost in antibodies a week after the shot, according to the preliminary study findings. Via The Washington Post:

Israel this week became the first country to launch a major second-booster campaign, making the fourth vaccination available to anyone 60 and older whose last shot was at least four months ago. Bennett’s office said more than 100,000 Israelis have registered or been vaccinated for their fourth shot in the two days of the campaign.

Critics had said the move was premature in the absence of data on a second booster’s safety and effectiveness. Some researchers didn’t rule out that repeat doses of the same vaccine could dampen the body’s immune response.

But the study, conducted by Israel’s Sheba Medical Center, could steer more policymakers toward an aggressive booster policy if it holds up to further analysis. Previous research from South Africa and Britain have suggested that omicron, while more infectious than other coronavirus variants, is less likely to cause serious illness in fully vaccinated individuals.

Some experts thought the campaign was premature:

Hagai Levine, an epidemiologist at Hebrew University and chairman of the Israeli Association of Public Health Physicians, applauded the government’s decision to offer the booster to those with compromised immune systems. But for healthy individuals, it was still unclear whether the immune effects of the first three Pfizer doses had waned so much that a fourth dose was called for, he said.

“It’s kind of the right answer to the wrong question,” Levine said of the new study results. “That it raises the antibody levels is good news, but first we need to know if there is a need for another shot.”