An Israeli hospital on Monday began a study to test the safety and effectiveness of a fourth dose of a Covid-19 vaccine, as health officials continued to deliberate over rolling out fourth shots for vulnerable people nationwide.
Officials at Sheba Medical Center, near Tel Aviv, said that their study was the first of its kind in the world and involved administering an additional shot to 150 medical personnel who had received a third dose of the Pfizer-BioNTech vaccine at least four months ago.
The moves in Israel, an early leader in Covid vaccinations, are being closely watched as governments worldwide struggle with how to confront the rapidly spreading Omicron variant, which is driving record numbers of new infections in parts of the United States, Europe and other places. Even as some studies suggest that Omicron infections are milder than those caused by other variants, the surges are already stretching health systems, and experts warn that it could lead to many more deaths.
With studies showing that Covid vaccines still protect people from getting seriously ill from Omicron, a panel of medical experts advising the Israeli government recommended last week that health officials offer a fourth shot for people ages 60 and older, for those with weaker immunity and for medical workers.
The proposal is awaiting formal approval from the Ministry of Health, but questions have been raised about whether the recommendation was premature given the lack of data on the effects of a fourth shot. It was unclear whether the ministry would wait for the results of the hospital study to make its recommendation.
The advisory panel acknowledged uncertainty over the effects of Omicron, but pointed to evidence of decreased immunity in people who were among the first to receive a third dose in August. Israeli data showed a doubling of the rate of infection from the Delta variant, then dominant, among the 60-plus age group within four or five months of the third shot.
Israel, a relatively small country with an efficient public health system, was a leader in introducing the first round of Covid vaccinations and later in giving booster shots, putting it in position to assess early how effective the shots are and how quickly the protection wears off.
Most of the advisory panel argued that the potential benefits of a fourth dose outweighed any risks, and that there was no time to lose in making decisions to protect those most susceptible. But other experts argued that not enough was known about the effects of a fourth shot, and some scientists have raised concerns that too many shots might cause a sort of immune system fatigue, compromising the body’s ability to fight the virus, particularly among older people.
A senior Health Ministry official said last week that the ministry would gather more data from other countries, especially about the risk of severe illness from Omicron among older people, before deciding on whether to offer a fourth dose, and to whom.
On Monday, a second ministry official said that a decision could come within days. Both officials requested anonymity to comment on the process.
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Also Monday, the Israeli Health Ministry formally accepted another of the recommendations of the advisory board, shortening the period between administering a third booster shot after the second vaccine to three months from five months.
“Now, in light of the Omicron wave, there is an increased need to boost the level of immunity among the general population as quickly as possible,” the ministry said in a statement, noting that other countries in Europe had done the same.
Most of Israel’s population has received at least two doses, but about a million eligible citizens have not yet received a third booster shot, out of a total population of nine million.