A fourth dose of Covid mRNA vaccine is not effective against Omicron infection, preliminary research from Israel has shown. Health Policy Watch has more.
“Despite a significant increase in antibodies after the fourth vaccine, this protection is only partially effective against the Omicron strain, which is relatively resistant to the vaccine,” lead researcher Prof Gili Regev-Yochay, told a media briefing on Monday.
Some 154 health workers at Sheba Medical Center received their fourth Pfizer shot two weeks ago. A week ago, 120 health workers received a shot of Moderna following three doses of Pfizer one week ago.
They were matched with a control group of around 6,000 health workers who have been being followed by the hospital since the start of Israel’s vaccination campaign in December 2020.
According to Regev-Yochay, the third dose resulted in “much higher antibodies, neutralisation and the antibodies were not just higher in quantity but also in quality” than the second dose – but the fourth vaccine did not show significant antibody increase.
“Maybe there are a few more antibodies but not much more compared to the third dose,” said Regev-Yochay.
Last week, she told Israeli Prime Minister Naftali Bennett that there had been a five-fold increase in antibodies in people who took the fourth dose, but she later told a radio station that “the amount of antibodies returns to the level it was after the third vaccine, not more. It’s nice, but it’s not what we expect from a booster”.
In addition, around the same percentage of hospital workers who received the fourth dose caught the virus as those who didn’t get the fourth booster.
With the UKHSA reporting three-dose protection against Omicron at under 50% after 10 weeks, this suggests a limit to what repeated shots of the same vaccine can achieve.
The findings come as Israel experiences a large surge in reported infections and ICU admissions, despite 65% of the country being at least double-dosed, 46% being triple-dosed, and some even quadruple-dosed. It will be interesting to see how this translates into deaths (how many of them are incidental admissions?), and what this might tell us about Omicron and vaccines.
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