The neutralizing ability of even three shots of the Pfizer corona vaccine is four times less against the Omicron than the Delta variant, according to researchers at Sheba Medical Center.
The team looked at the ability of serums of 40 vaccinated healthcare workers at Sheba to neutralize the Omicron variant – 20 who received the booster shot within the last month, and 20 who had only received two shots, the last one five or six months ago.
The study is based on the exclusive data available in Sheba as part of the large serology study conducted among health workers at the medical center. It was conducted in collaboration with the Health Ministry’s Central Virology Lab, which is located on the Sheba campus.
Those who received the second dose did not have any neutralization ability against the variant, while they continued to have some ability against Delta and even the original Wuhan strain.
“There was no neutralization ability whatsoever, and that is very worrisome,” said Dr. Gili Regev-Yochay, director of the Infectious Disease Epidemiology Unit at the hospital, in a briefing on Saturday night, adding that these people might also be exposed to serious disease.
It is also unclear if people who received two doses more recently would also be protected, she said.
Lab tests conducted in South Africa last week showed that antibodies from two shots of the Pfizer vaccine may be up to 40 times less effective against the Omicron variant.
In response to these studies, Dr. Sharon Alroy-Preis, head of Public Health Services, said in an interview with N12 Saturday night that the ministry is considering asking people to get their third dose as soon as three months after the second.
“People who have received the booster are better protected than those who received only the second, and of course, more than the unvaccinated,” Alroy-Preis said.
She noted that the only individual infected with the Omicron who is in serious condition is unvaccinated.
There are a million Israelis who have had two shots five or more months ago and have not gotten their boosters, she said, and another 325,000 who had two shots more recently and would be eligible for an earlier third dose if the policy changed.
“Two doses are not effective enough,” Alroy-Preis said.
On the other hand, the Sheba study found that the booster dose does increase the ability of the vaccine to work against Omicron by about 100-fold, meaning that there is “significant protection,” Regev Yochay said. “It is lower than the neutralizing ability against the Delta – about four times lower. But it is very optimistic.”
She added that “it looks like with Omicron there is a chance that people with the booster could get infected, but have much less chance of getting seriously infected.”
Regev Yochay said that it is still unclear whether the effectiveness of the booster shot will also decrease over time, and that this is something the Sheba researchers are looking into now.
The Israeli study, which should be stressed is a neutralizing antibody study done in the lab and not based upon real-world data, has been sent out for peer review.