GENEVA — A top World Health Organization expert on vaccines says people should feel reassured that even if health authorities turn up a link between blood clots and the AstraZeneca vaccine, such cases are “very rare.”

Dr. Kate O’Brien, who heads WHO’s department of immunizations and vaccines, said the U.N. health agency and the European Medicines Agency are trying to investigate the possibility of a link between blood clots and the AstraZeneca shots. The potential side effect has prompted some countries — mostly in Europe — to temporarily suspend use of the AstraZeneca vaccine.

A WHO committee on vaccines is looking into the issue.

“I think the reassurance to the public is that regardless of whether or not the committee ultimately assesses that there may be an association between these events and the vaccine, that in any event, these are very rare events,” O'Brien said during a Wednesday news conference.

The current “benefit-risk assessment” from the European Medicines Agency and WHO is for countries to continue giving people AstraZeneca shots, she said. Both WHO and EMA are expected to present updated recommendations on Wednesday or Thursday.

O’Brien said in general “vaccine recommendations are dynamic,” and are reviewed over days, months, and years. She noted that blood clots occur regularly in the population.

“What we don’t know is whether or not that experience would be related to having been vaccinated,” she said. “The important point is that if anybody is having symptoms, any serious medical symptoms, regardless of whether you’ve been vaccinated or not vaccinated, it’s important to seek medical care for the presence of those symptoms.”

The comments came at a news conference detailing how a WHO expert panel on vaccines recommended use of Johnson & Johnson’s one-dose COVID-19 vaccine, which has already been granted an emergency use authorization from the U.N. agency.

Dr. Annelies Wilder-Smith, a technical adviser to the expert panel, noted that studies on the J&J vaccine involving some 42,000 people turned up 10 cases of blood clotting in the placebo group — slightly more than half of all participants — and 14 cases among those who were administered the vaccine. She called that difference “not statistically significant.”