On Wednesday, both Denmark and Sweden announced that they are pausing the use of the Moderna vaccine in people less than 30 years old due to a rare but potentially dangerous cardiovascular side effect.

The decision to halt the vaccine came after data showed an increase in myocarditis among people under 30, particularly those who received the Moderna shot. According to Reuters, another study conducted in the US indicates that males under 20 who have had COVID are up to six times more likely to contract myocarditis. However, the study is still subject to peer review.

"The connection is especially clear when it comes to Moderna's vaccine Spikevax, especially after the second dose," said the Swedish Ministry of Health in a statement. "In the preliminary data ... there is a suspicion of an increased risk of heart inflammation when vaccinated with Moderna," concurred the Danish Health Authority in a similar statement.

The study in question is also still subject to a final assessment, and conclusive data is expected to be available within a month.

A spokesperson from Moderna also commented. "These are typically mild cases, and individuals tend to recover within a short time following standard treatment and rest. The risk of myocarditis is substantially increased for those who contract COVID-19, and vaccination is the best way to protect against this."

The Moderna vaccine, which US President Joe Biden recently received, was approved by the US FDA in late 2020 for emergency use and is considered 94 percent effective.