Israeli study shows fourth shot less effective on Omicron variant

Preliminary results show an additional COVID-19 vaccine booster shot not enough to prevent infection.

According to preliminary data from a trial conducted in Israel, while a fourth shot of a COVID-19 vaccine increases antibodies to a level higher than with the third shot, it was not adequate to prevent an Omicron infection. Last month, the Sheba Hospital commenced administering a fourth COVID-19 shot to more than 270 of its medical staff, all of whom had received three shots of Pfizer/BioNtech’s vaccine. Of these, 154 received the Pfizer/BioNtech shot and another 120 had received Moderna’s jab. While both groups showed increases in antibodies that were slightly higher than those from the third vaccine shot, these were however not high enough to prevent an Omicron infection. However, the country is still planning on pushing ahead with administering a fourth dose despite the results.

“Despite increased antibody levels, the fourth vaccine only offers a partial defense against the virus,” said Dr. Gili Regev-Yochay, director of the hospital's infection disease unit. “The vaccines, which were more effective against previous variants, offer less protection versus omicron." The results, while preliminary, will have notable implications not only for Israel’s own vaccination programme, but for the rest of the world as well as scientists scramble to determine whether there is any additional value in providing further booster shots. Israel, which was the fastest country to roll out vaccinations last year, began administering a second booster, to its most vulnerable and high-risk groups. Having been ahead of the curve in the fight against the pandemic, the country’s experience in combatting the virus has often set the tone for other countries.