On Tuesday, EMA vaccine strategy chief Marco Cavaleri said there was still no data supporting the need for a fourth COVID vaccine dose. And even if multiple boosters do prove to be necessary, they would need to be spaced out in the style of annual flu jabs, rather than delivered every several months. He also warned that overly frequent booster doses could potentially lead to “problems with immune response.”

“While use of additional boosters can be part of contingency plans, repeated vaccinations within short intervals would not represent a sustainable long-term strategy,” Cavaleri said at a media briefing. He also said boosters “can be done once, or maybe twice, but it’s not something that we can think should be repeated constantly.”

Growing resistance

The World Health Organization also said Tuesday that vaccination strategies “based on repeated booster doses of the original vaccine composition [are] unlikely to be appropriate or sustainable.” The WHO also repeated its frequently expressed warning that giving primary vaccinations to those in poorer countries was a higher priority, and urged vaccine makers to provide data on the vaccines they are developing to target new variants.

Pfizer CEO Albert Bourla said this week that it is still unclear whether fourth doses will be needed, while Israeli expert Eyal Leshem suggested “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.” The U.K.’s Health Security Agency said Friday that there was “no immediate need” for those who are not particularly vulnerable to get a second booster.

Despite the lack of supporting data, Israel has moved to fourth Pfizer/BioNTech doses for over-60s, health workers, and immunocompromised people. Bourla’s counterpart at Moderna, Stéphane Bancel, said last week that additional boosters could become necessary by the coming fall.

Endemic phase

In line with a sentiment that is starting to be expressed by European leaders, Cavaleri also said the rapid spread of the Omicron variant might help bring the continent out of the pandemic. “With the increase of immunity in population—and with Omicron, there will be a lot of natural immunity taking place on top of vaccination—we will be fast moving toward a scenario that will be closer to endemicity,” he said.

Also on Tuesday, professor David Heymann of the London School of Hygiene and Tropical Medicine said the U.K. was likely to become one of the first countries to emerge from the pandemic, with around 95% of the population now having antibodies against COVID that were gained via vaccination or infection.

Microsoft cofounder Bill Gates expressed much the same sentiment about endemicity in a Twitter Q&A on Tuesday, saying Omicron’s hectic passage through communities could allow them to treat COVID in much the same way as seasonal flu.

It is even possible that people might end up getting combined flu and COVID vaccines. Moderna’s Bancel said last September that his company (which had never released any drug before its COVID jab) was working on such a product.