Denmark on Monday became the first country to exclude Johnson & Johnson's COVID-19 shots from its vaccination program over a potential link to a rare but serious form of blood clot, Reuters reported.

The move comes after the country last month stopped using AstraZeneca's vaccine altogether citing similar concerns. 

The country's health authority said in a statement it had found that "the benefits of using the COVID-19 vaccine from Johnson & Johnson do not outweigh the risk of causing the possible adverse effect in those who receive the vaccine."

Excluding the J&J vaccine, which accounts for around a third of Denmark's total contracted supplies of COVID-19 shots, would delay the country's vaccination calendar by up to four weeks, it said.

"Taking the present situation in Denmark into account, what we are currently losing in our effort to prevent severe illness from COVID-19 cannot outweigh the risk of causing possible side effects in the form of severe blood clots in those we vaccinate," the health authority said.

It added that the vaccination rollout is progressing satisfactorily with other available vaccines.

The rollout of J&J's vaccine has also been delayed elsewhere in Europe over similar clotting concerns.