Fourth COVID Shot 'Only Partially Effective Against Omicron,' Initial Israeli Findings Suggest

A fourth shot of COVID-19 vaccine boosts antibodies to even higher levels than the third jab, but it likely is not enough to prevent omicron infections, according to a preliminary study in Israel.

The vaccines led to an increase in the number of antibodies "even a little bit higher than what we had after the third dose", said Prof. Regev-Yochay who leads the study at the Sheba Medical Center, adding that the results were preliminary and not yet published.

According to preliminary findings from the study, antibody levels a week after a third dose of the Pfizer vaccine was similar to that after a third shot, but researchers identified further increase after the first week. The study also found that antibody level were identical with Pfizer and Moderna vaccines a week after receiving the shot and that both vaccine were equally safe.

The protection offered by a second booster "is only partially effective against the omicron variant, which is relatively resistant to the vaccine," Regev-Yochay said.

Israel was the fastest country to roll out initial vaccinations a year ago and last month started offering a fourth shot, or a second booster, to the most vulnerable, high-risk groups.

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The Sheba study includes 270 health workers who were given a fourth shot of either the Pfizer or the Moderna vaccine, and a control group of employees who were not given a second booster at all.