Sweden and Denmark announced on Wednesday they will be pausing the use of the Moderna COVID-19 vaccine for younger age groups due to reported side effects.
Both countries point to rare possible side effects in young people from the vaccine, such as myocarditis and pericarditis, which causes inflammation in or around the heart, Reuters reported.
The Swedish health agency said it will stop giving the Moderna vaccine to those born in or after 1991, while Denmark will halt the vaccine's use for anyone under 18.
The two countries made the decision based on data from an unpublished Nordic study that still needs to be reviewed by the European Medicines Agency.
"The connection is especially clear when it comes to Moderna's vaccine Spikevax, especially after the second dose," the Swedish health agency said in regards to the risk of the rare side effects.
"In the preliminary data ... there is a suspicion of an increased risk of heart inflammation, when vaccinated with Moderna," the Danish Health Authority said.
Geir Bukholm, head of infection control at the Norwegian Institute of Public Health, said that especially men under the age of 30 should use the Pfizer-BioNTech vaccine over the Moderna one, according to Reuters.
Denmark had already mostly been using the Pfizer vaccine for those under 18.
The U.S. has only approved the Pfizer vaccine for minors, while Moderna's and Johnson & Johnson's are also used for adults.
Johnson & Johnson was the only one of the three to be temporarily suspended in the U.S. earlier this year due to rare blood clots.