The Centers for Disease Control and Prevention and the Food and Drug Administration said Friday that a possible link between stroke in adults 65 and older and Pfizer’s updated COVID-19 booster prompted an investigation.

A vaccine safety monitoring system detected a “safety signal” that Pfizer’s bivalent booster, which targets both the original strain of the virus from 2020 and the omicron subvariants BA.4 and BA.5, could be linked to an increased risk of ischemic stroke in those 65 and older. The agencies said, however, that subsequent analyses have not found an increased risk, indicating that the risk is low or nonexistent.

“There also may be other confounding factors contributing to the signal identified in the VSD that merit further investigation,” the agencies said in a statement. “It is important to note that, to date, no other safety systems have shown a similar signal and multiple subsequent analyses have not validated this signal.”

The potential risk that was identified in Pfizer’s vaccine was not seen with Moderna’s bivalent COVID-19 vaccine.

The FDA and CDC said they would continue investigating the early findings but concluded that there is no need to change vaccine recommendations. The CDC recommends that everyone 6 months and older stay up to date on their COVID-19 shots.

The FDA’s Vaccines and Related Biological Products Advisory Committee is expected to review safety data for Pfizer’s updated booster and other COVID-19 vaccines at a meeting later this month.