The Swedish health agency said on Wednesday it would pause using the shot for people born in 1991 and later as data pointed to an increase of myocarditis and pericarditis among youths and young adults that had been vaccinated. Those conditions involve an inflammation of the heart or its lining.

"The connection is especially clear when it comes to Moderna's vaccine Spikevax, especially after the second dose," the health agency said in a statement, adding the risk of being affected was very small.

Denmark said that, while it was already using the Pfizer/Biontech vaccine as the main option for people aged 12-17 years, it had decided to pause giving the Moderna vaccine to people below 18 according to a "precautionary principle".

"In the preliminary data ... there is a suspicion of an increased risk of heart inflammation, when vaccinated with Moderna," The Danish Health Authority said in a statement.

It referred to data from a yet unpublished Nordic study, which would now be sent to the European Medicines Agency (EMA) for further assessment. Final data was expected within a month, it added.

Sweden and Denmark said they now recommended the Comirnaty vaccine, from Pfizer/Biontech, instead.

Norway already recommends the Cominarty vaccine to minors and said on Wednesday that it was reiterating this, underlining that the rare side effects could happen particularly for boys and young men, and mainly after receiving a second dose.

"Men under the age of 30 should also consider choosing Cominarty when they get vaccinated," Geir Bukholm, head of infection control at the Norwegian Institute of Publica Health, said in a statement.

A Finnish health official said Finland expected to publish a decision on Thursday.

The EMA approved the use of Comirnaty in May, while Spikevax was given the nod for children over 12 in July.

Australian Associated Press