Top US health authorities said Friday they have not yet found a "causal" link between Johnson & Johnson's COVID-19 shot and blood clots, as the EU drug regulator probed possible instances among those who have received the vaccine.
"At this time, we have not found a causal relationship with vaccination and we are continuing our investigation and assessment of these cases," said a statement from the US Food and Drug Administration.
The regulatory agency said it was aware of "a few individuals" in the United States who had suffered clots and low levels of platelets in the blood after receiving J&J's vaccine.
"Both conditions can have many different causes," the FDA said. "We will keep the public updated as we learn more."
Four cases, one fatal, of rare clots with low blood platelets were reported among those vaccinated with the Johnson & Johnson shot, the European Medicines Agency (EMA) said in a statement.
There had been similar concerns over the UK's AstraZeneca vaccine, but experts have said benefits outweigh risks.