Israel's health ministry says it's found the small number of heart inflammation cases observed mainly in young men who received Pfizer's COVID-19 vaccine in Israel were likely linked to their vaccination.
Pfizer has said it has not observed a higher rate of the condition, known as myocarditis, than would usually be expected in the general population.
In Israel, 275 cases of myocarditis were reported between December 2020 and May 2021 among more than five million vaccinated people, the ministry said in disclosing the findings of a study it commissioned.
Most patients who experienced heart inflammation spent no more than four days in hospital and 95 per cent of the cases were classified as mild, according to the study, which the ministry said was conducted by three teams of experts.
The study found "there is a probable link between receiving the second dose (of Pfizer) vaccine and the appearance of myocarditis among men aged 16 to 30".
According to the findings, such a link was observed more among men aged 16 to 19 than in other age groups.
Pfizer said it was aware of the Israeli observations of myocarditis, noting no causal link to its vaccine had been established.
A US Centers for Disease Control and Prevention advisory group last month recommended further study of the possibility of a link between myocarditis and mRNA vaccines, which include those from Pfizer and Moderna.
CDC monitoring systems had not found more cases than would be expected in the population, but the advisory group said members felt healthcare providers should be made aware of reports of a "potential adverse event".
The Israeli ministry released the statement, which contained no recommendations, before a widely expected decision on whether to begin vaccinating youngsters aged 12 to 15 in Israel.