Fourth COVID vaccine shot less effective against Omicron – Study

The fourth shot of the COVID-19 vaccine can boost antibodies but provides insufficient protection against the Omicron variant, a new study has shown.

Early studies had suggested that two or three doses of COVID-19 vaccines may not be as effective against the Omicron variant.

Albert Bourla, Pfizer’s CEO said a fourth dose may be needed after preliminary research showed that the Omicron variant can undermine the antibodies generated by the COVID-19 vaccine.

However, the preliminary study from Israel’s Sheba Medical Center shows that a fourth shot of the Covid vaccine boosts antibodies to even higher levels than the third jab but it is not effective enough to prevent Omicron infections.

The Center gave the second booster shot in a trial among its staff, studying the effect of the Pfizer booster in 154 people after two weeks and the Moderna booster in 120 people after one week, according to Gili Regev-Yochay, director of the Infection Diseases Unit.

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These were compared to a control group that did not receive the fourth shot. Those in the Moderna group had previously received three shots of Pfizer’s vaccine, the hospital said.

The vaccines led to an increase in the number of antibodies “even a little bit higher than what we had after the third dose”, Regev-Yochay said.

“Yet, this is probably not enough for the Omicron. We know by now that the level of antibodies needed to protect and not to get infected from Omicron is probably too high for the vaccine, even if it’s a good vaccine.

“The bottom line is that the vaccine is excellent against the Alpha and Delta [variants], for Omicron it’s not good enough,” she explained.

Regev-Yochay however said a fourth shot can be given to those at higher risk, but that perhaps the current recommendations should be changed to only include older groups.

The centre noted that the study, which is the first of its kind in the world, is preliminary and not yet published.

Meanwhile, Israel has already rolled out second booster doses to offer eligible populations four doses in total.