Sweden and Denmark decided to pause vaccinations with Moderna Inc.’s Covid-19 shot for younger people because of potential side effects.
The Swedish health authority Wednesday cited new data on the increased risk of heart inflammation as a reason for the pause for those aged 30 and under. Denmark will stop giving the shot to those younger than 18.
Moderna shares fell as much as 5% in early trading in New York. The company didn’t immediately respond to a request for comment.
“We are monitoring the situation closely and are acting rapidly to ensure that Covid-19 vaccinations are constantly as safe as possible, while also providing protection,” said Anders Tegnell, Sweden’s chief epidemiologist.
Both countries recommended Pfizer Inc.’s and BioNTech SE’s rival vaccine as a replacement.
Sweden’s public health watchdog said a new preliminary analysis from the Nordic region indicates that the connection between vaccination and heart inflammation is clearest with the Moderna shot, especially after the second dose. The higher risk comes within four weeks of vaccination, and usually in the first two weeks, it said.
Those who have been vaccinated recently with a first or second dose of the Moderna vaccine shouldn’t worry, Tegnell said, as the risk is very small. Denmark’s National Board of Health indicated it hasn’t seen any differences in side effects between the two vaccines.
Both Moderna and Pfizer-BioNTech rely on messenger RNA technology to prompt an immune reaction. On Monday, the European Medicines Agency authorized the use of an extra dose of Moderna’s shot for those with a severely weakened immune system.
Last week, Slovenia temporarily halted another type of vaccine made by Johnson & Johnson after the death of a young woman who had received it. Earlier this year, a number of countries placed age restrictions on AstraZeneca Plc’s shot due to links with other potential side effects.
The Astra and J&J vaccines use technology called a viral vector that’s different from the mRNA shots.