The recommendation by an Israeli panel to administer a fourth vaccine to those who are over 60 is being met with a tepid response by some of the country's medical experts, who believe more data is needed.
"I supported the booster recommendation in July. But that time we had better evidence. Today, we don't have any good evidence," said Dr. Dror Mevorach, head of the coronavirus department at Hadassah University Hospital Ein Kare in Jerusalem.
"I think there is a great question about the impact of this fourth booster. I'm not sure it will help."
Mevorach told CBC News that unlike the decision to implement the third dose, which was met with wide approval, this recommendation is being questioned by some in the medical community.
"I would say that I got dozens of calls from both medical doctors and scientists saying to me that we think the same, that there's no evidence to give [a fourth dose] for the moment," he said.
Israel's PM welcomes recommendation
The recommendation for a fourth dose to people over 60, those with compromised immune systems and health-care workers was made based on concerns of waning immunity of the three vaccines already administered, combined with the potential threat of an Omicron outbreak seen in other countries.
"The price will be higher if we don't vaccinate," Boaz Lev, who heads the advisory committee, told reporters following the panel's decision.
The recommendation was also welcomed by Israeli Prime Minister Naftali Bennett, who called it "great news that will help us overcome the Omicron wave that is spreading around the world."
It is currently being reviewed by Israel's director general of the Health Ministry, Nachman Ash. If approved, Israel would become the first country to roll out a fourth dose to some of its citizens. However there have been some reports that Ash might be stalling while he reviewed information from Britain that shows that Omicron leads to less severe illness than the Delta variant.
Dr. Ron Dagan, a professor of pediatrics and infectious diseases at the Ben-Gurion University of the Negev and a member of the expert panel, acknowledged that the recommendation was not based on data of fourth dose results "because there is no data."
"There's no data that we could base on our recommendation," he told CBC News in a phone interview. "But on the other hand, there are data that altogether made us worried about what's going on as a potential scenario in the upcoming weeks."
There is evidence of waning immunity against infection about three to four months after the third vaccine was rolled out, he said.
'Scientific evidence is not there'
Dagan said the panel didn't believe a fourth shot would cause any harm, and it made an "educated guess" about Omicron's potential impact and the benefits and risks of offering a fourth dose.
"To the best of our judgment, the potential benefits, we believe, are bigger than the potential risks."
Mevorach said he respects the fact that some people believe that Israel is facing a potential catastrophe when it comes to Omicron and that they want to do everything they can.
"But I must say that medical or scientific evidence is not there," he said.
It may be better to wait for an Omicron specific booster, which both Pfizer-BioNTech and Moderna have indicated could be ready by March, he said.
Prof. Hagai Levine, an epidemiologist and chair of the Israel Association of Public Health Physicians, told the New York Times that while he respects the "better safe than sorry" opinion of the panel, "before giving a fourth shot, it is preferable to wait for the science."
Nadav Davidovitch, director of the Ben-Gurion University School of Public Health, said he would have offered a "weaker recommendation" than what was put forward by the expert panel.
Instead of a "forceful campaign" for another booster, he said he would rather allow people that are high risk to choose to have the fourth dose, "because we don't have enough data."
Cyrille Cohen, head of the lab of immunotherapy at Bar-Ilan University, said he understands how the panel reached its conclusion and that it was all about "risk managing."
"We see how [Omicron] is developing in other countries, and we are afraid that at some point, cases will explode in Israel," he said. "And then we might be in a situation where especially vulnerable people are not protected enough."
The problem, Cohen said, "is that we don't have a lot of data, and that's where I think it is a good thing that we gather right now a little bit more data."
Cohen said he wanted to make it clear that he wouldn't think of telling someone not to get the fourth shot.
"I would rather say, 'OK, we need more data.'"