A preliminary study in Israel, believed to be the world's first, showed that a fourth COVID-19 vaccine is not enough to prevent omicron infections.
Gili Regev-Yochay, director of the Sheba Medical Center's Infectious Diseases Unit, said the trial examined the effect of the Pfizer booster after two weeks and the Moderna booster after one week, according to Reuters.
Regev-Yochay said the increase in antibodies from a fourth shot "was probably not enough for Omicron."
"We now know that the level of antibodies needed to protect and not become infected with Omicron is probably too high for the vaccine, even though it is a good vaccine," she added.
Sheba Medical Center ran the trial on other booster shots among 150 of its employees, and its results were preliminary and unpublished, The Times of Israel reported. About 500,000 Israelis have been vaccinated with a fourth dose from Sunday.
Israel has led the push for vaccinations throughout the pandemic and was the first country to start offering booster shots to its population.
prime minister Naphtali Bennett previously announced that the country would begin offering one fourth vaccine as another booster shot for high-risk populations and vulnerable groups.
Despite pressure on vaccinations, Israel reported nearly 12,000 new COVID-19 cases earlier this month, a record-setting figures for daily case rates since the beginning of the pandemic.
"There is no control over the omicron wave," Sharon Alroy-Preis, the Israeli health ministry's senior public health official, told a local news source at the time.