In Israel, which has already started rolling out second boosters for those over 60, health workers, and the immunocompromised, infectious disease specialist Eyal Leshem reckons most people will be sufficiently protected against severe COVID with two or three doses.

“We may need to update those boosters every several years, possibly every year, to adjust them to the prevalent variant, but we may well not need any boosters if future variants prove to be less virulent, as we see with Omicron,” the Sheba Medical Center expert told CNBC. “So it is possible that people who have had two or three doses of the current vaccines, and then been exposed during this wave to Omicron, or are exposed during future waves to other less virulent variants, will not need another booster at all.”

Leshem also pointed out that Israel’s move into fourth-dose territory was based on “expert opinion” rather than “robust data as we would ideally like to have in clinical medicine.” Indeed, when the country announced the move, Pfizer and BioNTech—whose vaccine is by far the most widely used in Israel—suggested the deployment would provide useful data to indicate safety and efficacy.

Early days

There is already some small-scale interim data on the fourth dose’s safety and efficacy, coming from a trial at the Sheba Medical Center itself. Touted by Prime Minister Naftali Bennett a week ago, the data suggests the second booster is safe and leads to a fivefold increase in antibodies.

Moderna CEO Stéphane Bancel, whose company also makes a cutting-edge, mRNA-based COVID vaccine, said last week that a fourth dose would likely become necessary in the fall, as the efficacy of boosters will decline over a period of several months. He also said the British and South Korean governments had already placed their orders for this eventuality.

Counterpoint: The U.K.’s Health Security Agency said Friday that there was “no immediate need” for even older age groups to get a second booster, and Andrew Pollard—a key figure behind the Oxford/AstraZeneca vaccine—even went so far as to say regular boosters would not be “affordable, sustainable, or probably even needed” for those who are not particularly vulnerable.

And even some who stand to gain from expanding booster campaigns seem less than convinced. Pfizer CEO Albert Bourla struck a note of caution on Monday, when the pharma firm announced development of a “hybrid vaccine” targeting Omicron and earlier variants. Bourla said it remains unclear whether a fourth dose of the vaccine will be necessary, adding: “I don’t think we should do anything that is not needed.”

Wider implications

Rich countries’ blanket booster programs have massive implications for the wider pandemic, because they reduce the doses going to poor countries where most people haven’t even received primary vaccinations, leaving them vulnerable to severe disease and death.

Former U.K. Prime Minister Gordon Brown recently called such programs “a stain on our global soul,” and the World Health Organization has warned that they are “likely to prolong the pandemic [by] giving the virus more opportunity to spread and mutate.”