Sweden is pausing use of Moderna’s coronavirus vaccine for people under the age of 30 following reports of possible rare side effects, including myocarditis, the country’s health agency announced Wednesday, describing the move as “precautionary.”
In an announcement posted online, Swedish health authorities cited “signals” of an increased risk of myocarditis (heart muscle inflammation) and pericarditis (inflammation of the membrane surrounding the heart) among Moderna vaccine recipients.
The diseases—marked by symptoms like chest pain and shortness of breath—are most common among young men, and while they typically clear up within a few weeks, can in a small number of cases become chronic.
The agency did not say how many possible cases of the rare heart inflammation it has identified, but described the number as “very small” and the side effects as “very rare.”
People in this age group are now recommended to get the Pfizer-BioNTech vaccine (the Swedish health agency recommended children between 12 and 15 receive only the Pfizer vaccine earlier this week).
Despite their rarity, myocarditis and pericarditis became a source of concern in the Covid-19 pandemic due to a small number of cases of people developing the heart diseases after getting vaccination. However, these cases were extremely small compared to the number of people who got jabs and safety groups quickly ruled the benefits of the vaccine outweighed the risks of the disease. Furthermore, research has suggested people are much more likely to develop myocarditis after contracting Covid-19 than they are after getting the vaccine. A Centers for Disease Control and Prevention (CDC) study published last month recorded a big spike in cases of myocarditis last year driven by a significant “association” between the rare heart disease and Covid-19, though it was still extremely uncommon for anyone “without or without” the coronavirus.