Fourth Pfizer jab ineffective in blocking Omicron, Israeli study shows

A fourth dose of the BioNTech/Pfizer vaccine is largely ineffective in stopping Omicron infections despite boosting antibodies, an Israeli hospital study showed.

Healthcare workers at the Sheba Medical Center who received a fourth dose of the vaccine continued to get infected even though blood tests showed an increase in two key kinds of antibodies, according to professor Gili Regev-Yochay who led the research.

The preliminary findings, which are yet to be published, add to the global debate about the effectiveness of repeat doses of the Covid vaccine after booster shots, as concerns grow that regular shots are unsustainable in the long term.

Just over 150 members of the Tel Aviv hospital received fourth doses of the Pfizer vaccine, part of an ongoing experiment where thousands of Sheba employees have had regular serology tests — which look for antibodies in blood that fight infection — beginning from before their first doses in December 2020 to track the vaccine’s efficacy.

Enough of them tested positive for coronavirus two weeks after their fourth jabs to indicate that the level of antibodies needed to protect against infection from Omicron was “probably too high” for the vaccine to induce, said Regev-Yochay.

The preliminary findings were important enough to be shared early with policymakers, she said. Debate continues worldwide on the need for booster shots for the double and triple-jabbed. Meanwhile billions in poorer countries are still waiting for their first shots.

The fourth shot proved to be less of a jolt to antibody levels than the third, which itself was more effective than the second in the amount and quality of antibodies produced, said Regev-Yochay.

“The decision to allow the fourth vaccine to vulnerable populations is probably correct and it may give a little benefit — but not enough to support the decision to give it to all of the population,” she said.

Close to half a million Israelis above the age of 60 have opted to receive a fourth shot, most within 12 or 13 months of receiving their first shots in December 2020 when Israel led the world in vaccinating its population against the Alpha variant.

In July, Prime Minister Naftali Bennett used a third shot to avert lockdowns as the Delta variant threatened to engulf the country’s medical system when it became clear that the efficacy of Pfizer shots dipped within months.

Israel was is nearing a peak of Omicron infections, health officials predicted, with so many new cases a day that the health ministry’s website crashed. Bennett said the high numbers reflected widespread testing, telling the World Economic Forum on Tuesday that some 5 per cent of Israelis were being tested every day.

“That’s why the case numbers are so high, not because necessarily so many people are infected,” he said.

Bennett has personally championed the fourth shot, making it the bulwark of his attempts to keep Israel open despite tens of thousands of new cases every day. He has cut mandatory isolation to five days, and the government will pay the wages of those in quarantine.

It will also continue the use of fourth shots, especially among the elderly, despite the data from Sheba hospital, the health ministry’s director-general Nachman Ash told Army Radio on Tuesday.

“Protection from serious morbidity, especially for the elderly population and at-risk population, is still afforded by this dose, and therefore I call on people to keep coming to get vaccinated,” he said.

Another group of Sheba health workers received the Moderna vaccine as their fourth dose after their three initial doses of the Pfizer vaccine, but preliminary results from that study, still to be completed, were similarly unpromising, said Regev-Yochay.

“If we were still in the Delta or Alpha pandemic, then we would be in a much better state,” she said. “But since Omicron is so infectious and much more resistant to the vaccines — we are in a different state.”