Fourth Dose Vaccine Less Effective Against Omicron Variant, Researchers: Required Antibody Level Is Too High

JAKARTA - Researchers say that it is possible that high antibodies are needed to avoid infection with the Omicron variant, making the fourth dose of the COVID-19 vaccine less effective.

The fourth dose of the COVID-19 vaccine raised antibodies to a higher level than the third shot, but it was not enough to prevent Omicron infection, according to a preliminary Israeli study.

The Sheba Israel Medical Center has administered a second booster shot in a trial among its staff, studying the effects of the Pfizer booster on 154 people after two weeks, as well as the Moderna booster on 120 people after one week, said Gili Regev-Ychay, director of the Infectious Diseases Unit.

This was compared to a control group that did not receive the fourth shot. Those in the Moderna group had previously received three injections of the Pfizer vaccine, the hospital said.

Regev-Yochay said the vaccine caused an increase in antibody counts, "even slightly higher than what we had after the third dose."

"However, this may not be enough to deal with the Omicron variant," he told reporters, as quoted by Reuters January 18.

"We know now that the antibody levels needed to protect against infection from Omicron variants may be too high for a vaccine, even though it's a good vaccine," he said.

However, the findings, which the hospital says are a world first, are preliminary and have yet to be published.

To note, Israel was the fastest country to launch an initial vaccination against COVID-19 a year ago. Last month, they began offering a fourth injection, or a second booster, to the most vulnerable and high-risk groups.