A vial labelled "Moderna COVID-19 Vaccine" is seen in this illustration taken January 16, 2022.
A vial labelled "Moderna COVID-19 Vaccine" is seen in this illustration taken January 16, 2022. Reuters / DADO RUVIC

The European Medicines Agency (EMA) is recommending Novavax's COVID-19 vaccine carry a warning of two types of heart inflammation, based on a small number of reported cases, an added burden for a shot that has failed to win wide uptake.

The conditions - myocarditis and pericarditis - should be listed as new side effects in the product information for the vaccine, Nuvaxovid, the EMA said on Wednesday.

The U.S. Food and Drug Administration flagged a risk of heart inflammation from the Novavax vaccine in early June.

Myocarditis and pericarditis were previously identified as rare side effects, mostly seen in young men, from the established mRNA vaccines made by Moderna and the Pfizer-BioNTech alliance with the vast majority of those affected recovering fully.

The EU agency said on Wednesday it asked U.S. vaccine developer Novavax to provide additional data on the risk of these side effects occurring. Novavax did not have an immediate comment.

Last month, the EMA identified severe allergic reactions as potential side effects of the vaccine.

Novavax was hoping that people who have opted not to take Pfizer and Moderna's vaccines - which are based on the groundbreaking messenger RNA (mRNA) technology - would favour its shot because it relies on technology that has been used for decades to combat diseases including hepatitis B and influenza.

However, only around 250,000 doses of Nuvaxovid have been administered in Europe so far since its launch in December, according to the European Centre for Disease Prevention and Control.