Due to reports of a rare cardiovascular side effect, Finland halted the use of Moderna’s COVID-19 vaccine for younger boys on Thursday, joining Sweden and Denmark in doing so.

Finland will instead deliver Pfizer’s vaccination to men born in 1991 and after, according to Mika Salminen, director of the Finnish health institute. Finland provides vaccinations to everyone aged 12 and up.

“According to a Nordic study comprising Finland, Sweden, Norway, and Denmark, males under the age of 30 who received Moderna Spikevax had a slightly increased risk of having myocarditis than other men,” he stated.

On Wednesday, Swedish and Danish health officials declared that the Moderna vaccination would be halted for all young adults and children, citing the same unpublished study.

On Wednesday, Norwegian health officials reaffirmed that men under the age of 30 should choose Pfizer’s vaccine.

The Nordic study will be published in a few weeks, according to the Finnish institute, and preliminary data had been given to the European Medicines Agency (EMA) for review.

The EMA’s safety committee concluded in July that such inflammatory heart conditions could occur in very rare cases following vaccination with Spikevax or the Pfizer/BioNTech Comirnaty jab, more often in younger men after the second dose.

Regulators in the United States, EU and the World Health Organization have however stressed that the benefits of shots based on the mRNA technology used by Moderna and Pfizer-BioNTech in preventing COVID-19 continue to outweigh the risks.

A Moderna spokesperson said late on Wednesday it was aware of the decisions by the Swedish and Danish regulators.

“These are typically mild cases and individuals tend to recover within a short time following standard treatment and rest. The risk of myocarditis is substantially increased for those who contract COVID-19, and vaccination is the best way to protect against this.”

Italy’s Health Minister Roberto Speranza told reporters Italy was not planning to suspend the Moderna vaccine and said European countries should work together more closely to coordinate better.

“We have to trust international authorities, starting with EMA which is our reference agency and has expressed very clear judgments on the matter,” he said.