Because of the increased risk of heart inflammation, a very rare side effect associated with the COVID vaccine, Scandinavian authorities suspended or discouraged young people from getting the Moderna shot.

Sweden suspended the use of Moderna for recipients under 30, while Denmark said they wouldn't offer it to those under 18. Norway urged residents under 30 to get the Pfizer vaccine instead. According to Dr. Hanna Nohynek, chief physician at the Finnish Institute for Health and Welfare, Finnish authorities are expected to announce their decision Thursday.

Denmark, Norway, and Finland based their decision on an unpublished study with Sweden's Public Health Agency, reported CP24. They said it signaled "an increased risk of side effects such as inflammation of the heart muscle or the pericardium." Though it added, the risk of being affected is "very small." The study's final results are expected in about a month and are under review by the European Medicines Agency's adverse reaction committee.

Anders Tegnell, Sweden's chief epidemiologist, said they "follow the situation closely and act quickly to ensure that vaccinations against COVID-19 are always as safe as possible and at the same time provide effective protection" against the virus. Adults have already received hundreds of millions of Moderna doses.

In July, the European Medicines Agency recommended the Moderna vaccine for children ages 12 to 17, the first time the shot has been approved for people under 18. Moderna's vaccine received the go-ahead for use in adults across the 27-nation European Union in January.

In a separate study on 3,700 children over 12, the vaccine triggered the same signs of immune protection. No COVID diagnoses arose in the vaccinated group compared with four cases among those given dummy shots. Young vaccine recipients, like adults, reported sore arms, headache and fatigue, as the most common side effects.

But US and European regulators cautioned that both the Moderna and Pfizer vaccines appeared to use a rare reaction in teenagers and young adults, including chest pain and heart inflammation. The Moderna shot is licensed in Britain, Canada, and the US, but not to children under 12. Canada approved its use for those over 12, while Pfizer approved for children under 18 in Europe and North America.

Swedish health authorities said the heart symptoms "usually go away on their own," but afflicted patients must have a doctor assess them. In 2019, approximately 300 people under 30 caught myocarditis and needed treatment. The conditions are more common among young men.

The preliminary Nordic analysis indicated the risk of myocarditis is apparent from the Moderna vaccine, especially after the second dose, the agency said. "The increase in risk is seen within four weeks after the vaccination, mainly within the first two weeks," it added.

Sweden recommended the Pfizer vaccine for these age groups instead. Its decision to suspend the Moderna vaccine is valid until December 1. In Denmark, residents under 18 won't receive the Moderna vaccine on suspicion of an increased risk of heart inflammation when vaccinated with Moderna shots.

Norway urged young people under 30 to get the Pfizer vaccine instead "due to an increased risk of a rare side effect" with Moderna. Denmark also recommended Pfizer but extended that to children ages 12-17 too.

"Based on the precautionary principle, we will in future only invite children and young people to receive this vaccine, not least [because] it is for this vaccine that the largest amount of data from use exists for children and young people, especially from the USA and Israel."