A preliminary study from Israel showed that even the fourth dose of Pfizer's COVID-19 vaccine (2nd booster shot) had limited effectiveness in preventing omicron mutation infection.

Israeli local media reported that the Sheba Medical Center, Israel's largest medical institution, announced the results of this investigation on the 17th local time, when 150 medical staff received the Pfizer vaccine's second booster shot test.

As a result of the investigation, the antibody level 1 week after the 4th inoculation was higher than 1 week after the 3rd inoculation.

However, the researchers concluded that this level of antibody was not sufficient to prevent omicron-mutated infection.

Dr. Gili Regev-Yohhai, head of the hospital's fourth dose of COVID-19, said, "Previously emerged vaccines that were very effective in preventing mutant infections were less effective in preventing omicron mutations."

He added, "(After the 2nd booster shot inoculation), I confirmed that the antibody increased more than the 3rd inoculation."

Dr. Regev-Ohavi said that although this study is a preliminary study that looked at early-stage data, "it is not lacking in providing basic data of interest to the public."

Israel approved the fourth dose last month after review by the vaccine advisory committee for immunocompromised and elderly people living in nursing homes, and then expanded the target to all seniors aged 60 and over and medical staff.

So far, more than 500,000 people in Israel have completed their fourth dose of the COVID-19 vaccine.