The World Health Organization says there is no evidence that COVID-19 mRNA vaccines increase the risk of strokes in older people.

WHO officials say there is no basis to the recent concerns raised by the media and science communities about the safety of the mRNA booster shots. They say the concerns, which are related to one U.S. data system that monitors safety, presented misinformation about deaths related to COVID-19 infection.

Kate O’Brien, WHO director of Immunization, Vaccines and Biologicals, said other U.S. and national vaccine safety monitoring systems have not found further evidence that mRNA vaccines lead to strokes.

“At this point in time, the best evidence is that there is no true association between the booster doses of Pfizer in the older adults and strokes,” she said. “And, again, there is an ongoing, unending system to continuously monitor safety, not only for COVID vaccine and dose-by-dose, but also for all other vaccines.”

O’Brien said COVID-19 vaccines are highly effective at preventing hospitalization, severe disease, or death, but less effective at stopping people from getting infected and transmitting the disease.

She noted it is particularly important that people in high priority groups receive all their recommended doses. They include people over age 60, those who have underlying medical conditions or are immunocompromised, pregnant women and health workers.

“For the strains that we have circulating in the world now, the omicron strains, the first booster dose actually improves the performance of your primary series for protection against the severe end of the disease spectrum,” O’Brien said. “So, you actually need three doses to get that optimal protection from vaccines.”

O’Brien said there is no direct evidence of the performance of the monovalent or bivalent vaccines on the XBB.1.5 strain of COVID-19. Since there currently is no data on whether the newer bivalent vaccines are more effective than ancestral vaccines, she said the WHO recommends both for booster doses.

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