Late Tuesday, an expert panel recommended a second booster for those over 60, immunosuppressed people, and health care workers. The move still needs to be approved by Israel’s health ministry, but Prime Minister Naftali Bennett was quick to welcome the advice, tweeting: “This is wonderful news that will assist us in getting through the Omicron wave that is engulfing the world.”

Israel has throughout the last year leaned heavily on the Pfizer-BioNTech mRNA vaccine. July’s decision to start rolling out third doses followed early data from the companies that indicated a significant increase in immune protection. However, this time round, no such data has been announced.

Nevertheless, Omicron infection numbers are typically doubling in about three days, which is extraordinarily fast. Pfizer CEO Albert Bourla said this month that the variant’s antibody-evading skills could mean a fourth vaccine dose is needed within a shorter time frame than the 12 months previously anticipated.

“We don’t really have data yet on the level of immunity, like we did when we decided on the third dose, but on the other hand, there is really scary data out there in the rest of the world,” expert panel member Galia Rahav reportedly said on Israeli radio Tuesday evening. “In a situation like this, if you don’t act immediately, you miss the train.” 

A Pfizer spokesperson said the U.S. firm and Germany’s BioNTech plan to study the effects of additional doses—of both the current vaccine formulation and an Omicron-specific version—in a clinical setting. The spokesperson added that Pfizer would continue to “evaluate real-world data, including wide use of a fourth dose”, suggesting that Israel’s unprecedented move will in effect provide the data to judge a fourth dose’s safety and efficacy.

Israel recorded over 1,300 new COVID cases on Monday, which was the highest tally since October. As of Tuesday, there were just over 340 confirmed Omicron cases, with over 800 further cases suspected but not yet confirmed. Israel also saw its first Omicron-related death on Tuesday, although doctors said that “stemmed mainly from pre-existing sicknesses and not from respiratory infection arising from the coronavirus.”

Anti-Omicron measures

Earlier this week, Israel banned most travel to and from the U.S., Canada, Italy, Germany, Belgium, Portugal, Hungary, Turkey, and Switzerland, owing to nearly a fifth of new COVID cases identified as having come from abroad.

On Tuesday, apart from recommending a fourth dose, the expert panel also approved measures limiting the number of shoppers who can enter shopping centers and requiring employees in large shops to have a “Green Pass” COVID vaccination certificate—a common requirement for entry into restaurants and other nonessential facilities, that has since October been valid only if the carrier has had a booster.

However, while Israeli data confirmed in October that third doses confer a huge benefit, and yet more Israeli data suggested earlier this month that two shots of Pfizer-BioNTech provide “almost no neutralizing ability” against Omicron six months after being administered, only 45% of the population has received a booster thus far.

The ethics and logic of booster shots are, at this time, far from clear-cut. While they do appear to be a crucial tool for keeping Omicron’s symptoms at bay, the widespread rollout of boosters in rich countries is already having a negative impact on the rollout of primary doses—without which people are much more vulnerable to illness—in poorer countries.

Since vaccines first became available a year ago, the developing world has struggled to secure vaccine supplies owing to rich countries’ hoarding of doses and refusal (particularly in Europe) to loosen intellectual property rules to increase production. That trend appears to be continuing in this new phase of the pandemic, and experts fear it could contribute to the emergence of further variants.

Update: This article was updated on Dec. 23 to include the Pfizer spokesperson’s quote.