France has become the fifth European nation to recommend people aged under 30 against using the Moderna COVID-19 vaccine due to concerns over the risk of myocarditis -- a rare heart inflammation.

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The nation's Public Health Authority (Haute Autorite de Sante) said those under age 30 should get the Pfizer-BioNTech COVID vaccine instead of the Moderna jab, Daily Mail reported. Previously, Denmark, Iceland, Finland and Sweden had either restricted or recommended against the use of the Moderna vaccine in young adults.

Even after rising concerns about the vaccine in Europe, the US Food and Drug Administration (FDA) has stood by its authorisation of the shots. "Within the population aged under 30, this risk appears to be around five times lesser with Pfizer's Comirnaty jab compared to Moderna's Spikevax jab," Haute Autorite de Sante has said.

The health department does not have any authority to ban drugs but can recommend against using them. In October, Sweden became the first country to pause the use of the Moderna COVID-19 shot in everyone born after 1990.

According to Sweden's Public Health Agency, data signals "an increased risk of side effects such as inflammation of the heart muscle or the pericardium" -- the double-walled sac containing the heart and the roots of the main vessels. However, it added that "the risk of being affected is very small".

Earlier this month, the Finnish Institute for Health and Welfare said that authorities won't give the vaccine to males under age 30, and they will be offered the Pfizer-BioNTech immunisation instead, also citing the heart inflammation data. Myocarditis and pericarditis, both types of inflammation of the heart, are known side effects of the COVID vaccines, and the Centers for Disease Control and Prevention (CDC) even warns that the condition may develop in young males after vaccination.

Last month, data on the Moderna vaccine's likelihood to cause heart inflammation was presented to a CDC advisory panel. The presentation showed that males were much more likely to develop the condition than females -- with those aged 18 to 24 at most risk, and the 25 to 29 group at risk as well.

For every one million doses of the Moderna shot administered, there are 13.3 more cases of myocarditis detected compared to every one million of the Pfizer jab, showed the data. The reason for this is now yet known.

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