The European Union’s vaccine regulatory agency warned that repeated use of COVID vaccine boosters could impair the booster recipient’s immune response, potentially “overloading” the immune system.

Speaking at a press briefing Tuesday, members of the European Health Medicines Agency’s Biological Health Threats and Vaccines Strategy committee discussed proposals to use a fourth dose of the COVID vaccine, following the decision by Israel to offer a second booster shot to elderly citizens and healthcare workers.

Marco Cavaleri, chief of the agency’s vaccines committee, warned against the overuse of booster shots, saying they cannot be “repeated constantly.”

“We are rather concerned about a strategy that entangles repeated vaccinations within a short term.”

“We cannot really continuously give booster doses every 3-4 months.”

Boosters “can be done once, or maybe twice, but it’s not something that we can think should be repeated constantly,” Cavaleri continued.

“There are two concerns here: If we have a strategy in which we give boosters, let’s say, every four months approximately, we will end up potentially having problems with the immune response, and the immune response may not be as good as we would like it to be. So we should be careful in not overloading the immune system with repeated immunization.”

“And secondly, there is the risk of fatigue in the population with the continuous administration of boosters.”

Cavaleri also said that he believes the time has come to treat SARS-CoV-2 as being endemic, rather than as a pandemic.

“We need to think about how we can transition from the current pandemic setting to a more endemic setting.”

Despite the agency’s warning Tuesday, on Wednesday, Denmark became the first European country to offer a fourth dose of the COVID jab, offering the second boosters to high risk groups, including the elderly.