A fourth dose – second booster shot — of the Pfizer Covid-19 vaccine protects people over age 60 three times more against serious illness and about two times more against infection compared with three doses.

This is the conclusion of a preliminary data analysis performed by a team of researchers from Israel’s Ministry of Health, Weizmann Institute of Science, Technion-Israel Institute of Technology, Hebrew University, and Gartner Institute at Sheba Medical Center.

In early January, considering the rapid spread of the Omicron variant, a fourth dose of the vaccine was made available to Israelis aged 60 and over and to at-risk populations and healthcare workers. As of January 23, 592,510 Israelis have received the fourth dose.

The study looked at data from about 400,000 four-dose vaccinees and about 600,000 three-dose vaccinees, all over the age of 60.

The ministry said these preliminary results will be updated over time with additional follow-up data.

On January 18, ISRAEL21c reported that preliminary results of Sheba’s world-first study of the fourth dose indicate it is not effective enough against the current Omicron variant of the SARS-CoV-2 virus.

Dr. Gili Regev-Yochay, chief of Sheba’s Infectious Disease Unit, said that the second booster caused “a pretty nice increase in the number of antibodies – even a little higher than we had after the third dose – yet this is probably not enough for the Omicron.”

Regev-Yochay supports the Israeli government’s decision to offer a fourth vaccine to vulnerable populations since “it may give a little benefit. But probably not enough [benefit] to support a decision to give it to all of the population.”