Fourth Pfizer COVID-19 shot less effective on Omicron, Israeli trial suggests

• Preliminary data found the second booster did increase antibodies

• Those with fourth shot only slightly less likely to get Omicron

A fourth shot of the COVID-19 vaccine manufactured by Pfizer Inc (NYSE: PFE) and BioNTech boosted antibodies further than the third dose but is insufficient to prevent Omicron infections, according to preliminary trial data conducted in Israel.

Gili Regev-Yochay, the director of the Infectious Diseases Unit at Israel’s Sheba Medical Center, on Monday, said that the hospital had inoculated its medical staff with a second booster shot.

Israel’s largest hospital is currently studying the effect of the Pfizer booster in 154 volunteers after two weeks and the Moderna Inc’s (NASDAQ: MRNA) booster in 120 people after one week.

The results from the volunteers 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.

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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 Regev-Yochay, the trial’s lead researcher.

“Yet, this is probably not enough for the Omicron,” she said. “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.”

However, she also mentioned that although the vaccines that were more effective against previous variants offer less protection with Omicron, those infected in the trial had only slight symptoms or none at all.

Israel as testing ground

Israel is finding itself a global test case time and again, as it begins widely delivering fourth doses amid a surge in the Omicron variant.

The country’s pandemic experience is being studied worldwide because of the government’s aggressive steps in containing the virus at the outset and the rollout of the world’s fastest coronavirus vaccination program, along with the early administration of boosters.

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With a technologically advanced public health system and small size, Israel signed a deal with Pfizer to provide data to demonstrate the impact of the vaccine on an entire population.

The middle-eastern nation started rolling out the fourth dose of the vaccine to the over-60s and immunocompromised in late December amid a surge in cases and have administered over half a million extra booster doses.

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