European Union regulators warn that frequent Covid-19 booster shots could adversely affect the immune system and may not be feasible.
Repeat booster doses every four months could eventually weaken the immune system, according to the European Medicines Agency.
Countries should leave time between booster programs and tie them to the onset of the cold season in each hemisphere.
It follows the blueprint set out by influenza vaccination strategies. This is according to the agency.
The advice comes as some countries consider the possibility of offering people second booster shots. This is in a bid to provide further protection against surging omicron infections. Earlier this month Israel became the first nation to start administering a second booster dose.
It is also administering the fourth shot to those over 60.
The U.K. said that boosters are providing good levels of protection and there’s no need for a second booster shot at the moment, but will review data as it evolves.
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On Tuesday, EMA vaccine strategy chief Marco Cavaleri said there was still no data supporting the need for a fourth COVID vaccine dose.
Even if multiple boosters are necessary, there will be a 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.”
The World Health Organization stated 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 priority.
It urged vaccine makers to provide data on the vaccines they are developing to target new variants.