Health-Worker Risks of Catching Omicron Half as Likely after Fourth Dose – Second Israeli Study Challenges Earlier Results
Israeli couple receives fourth dose of COVID vaccine in Israel
Israeli couple receives fourth dose of COVID vaccine in Israel

In still evolving data, yet another Israeli study has found that health workers who received a fourth dose of a Pfizer mRNA vaccine were half as likely to contract Omicron seven days after receiving the shot in comparison to people who only got three doses.  The study released Thursday came less than one week after another major hospital research center cast doubt on the effectiveness of the extra jab after providing it to several hundred health workers in a controlled clinical trial.

The evolving data reflects some of the ongoing debate among experts the world over over the effectiveness of additional doses of the same vaccine against the current variant wave – something few countries and hospitals have tested so far outside of Israel.

Tel Aviv Sourasky Medical Center released data from its real-world study of 6,863 medical workers who were vaccinated with a third dose of the Pfizer coronavirus vaccine between August and December 2021 and had not previously been infected with corona, including 1,316 workers who received the fourth dose as of January 3, 2022. During this period, 608 workers tested positive – but only 42 of them were diagnosed with the virus seven days or more after receiving the fourth vaccine.

From the analysis of the data using a regression model, the hospital concluded that “the risk of contracting the virus is twice as low seven days after receiving the fourth dose.”

Tel Aviv Sourasky Medical Center reveals real-world results of fourth dose campaign
Tel Aviv Sourasky Medical Center reveals real-world results of fourth dose campaign, showing that medical workers who took the shot were half as likely to contract COVID after seven days.

However, Sourasky added in a press release, these results “must be interpreted with caution” due to the short follow-up period of just 15 days after innoculation.

Other trial tested both Pfizer & Moderna

Sourasky’s report comes only days after Sheba Medical Center at Tel Hashomer shared preliminary results of its Helsinki-approved fourth shot clinical trial, indicating that a fourth dose of Pfizer or Moderna does not provide enough of a boost to significantly protect against Omicron.

Prof Gili Regev-Yochay, who is leading Sheba’s research on the matter, told reporters on Monday that two weeks after receiving a fourth Pfizer vaccine and one week after receiving a fourth Moderna jab that “the increase in antibodies is nice” but not enough to stop infection.

Some 154 medical workers from Sheba are participating in a trial of the a fourth Pfizer vaccine and another 120 in the Moderna arm of the experiment.

Although Regev-Yochay would not share numbers, she said that only slightly fewer people who received the fourth dose caught coronavirus than those in a control group, who were fully vaccinated with two shots and a booster.

Majority of seriously ill or hospitalized people continue to be those who are unvaccinated at all

In all cases, the researchers have stressed that while Omicron might break through the vaccines more than previous strains, the vaccines continue to stop severe disease. Regev-Yochay said that none of the study participants who got Omicron developed a severe or life-threatening case and the majority of serious patients in Israeli hospitals continue to be unvaccinated or people vaccinated with only two shots more than six months ago.

Israel’s Health Ministry approved giving a fourth shot for immunocompromised people in late December and soon after expanded its decision to include people over the age of 60 and medical workers. So far, more than half-a-million citizens have taken the fourth dose.

A handful of other countries have also approved offering its citizens fourth doses, including Greece, Chile and Brazil, though no other countries have started full campaigns nor released research on the effectiveness of the protocol.

The World Health Organization has spoken out against fourth shots, saying earlier this month that “a vaccination strategy based on repeated booster doses of the original vaccine composition is “unlikely to be appropriate or sustainable.”

But WHO’s Chief Scientist Dr Soumya Swaminathan also has said that more studies are needed to understand the duration of protection in different population groups after vaccines and boosters.  And, rather than pursuing boosters or vaccines for each new variant, she has called for R&D into vaccines that can hit at all “beta-coronaviruses”.

And rather than develop more variant-specific vaccines, Swaminathan and other leading vaccine experts, such as Peter Hotez of Texas Children’s Hospital have said work should be focused on more broadly neutralizing beta coronavirus vaccine – hitting not only at SARS-CoV2 but other SARS or SARS-like viruses that are circulating in the wild and likely to emerge at a later date.

Image Credits: Maccabi Health Services, Tel Aviv Sourasky Medical Center.

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