Novavax found to have lowered COVID risk but raises risk of heart inflammation: FDA

"These events raise the concern for a causal association with this vaccine, similar to the association documented with mRNA COVID19 vaccines," commented an FDA spokesperson.

"Based on the efficacy estimate in the clinical trial of this vaccine, it is more likely than not that the vaccine will provide some meaningful level of protection against COVID-19 due to Omicron, in particular against more severe disease," the FDA spokesperson continued.

Myocarditis has also been found to be a rare but possible side effect in mRNA-based vaccines such as those offered by Pfizer and Moderna, according to Reuters.

The announcement comes as the result of a massive 30,000-patient clinical trial which ran from December 2020 through September 2021. There were four cases of otherwise-unexplained myocarditis flagged in the study, all of them happening in the 20-day period following vaccination.

The FDA further iterated that Novavax has not yet agreed to flag myocarditis or the similar pericarditis as potential side effects of the vaccine, despite the agency's requests to do so.

"Despite the wide availability of authorized or approved vaccines, the SARS-CoV-2 pandemic is not well controlled in the U.S. ... there remains a desire for vaccines that have been developed using well-understood technology platforms," stated a spokesperson for the Novovax company.

It's important to note that the study was conducted largely before the Delta variant hit, and completely before the Omicron variant did. As such, it didn't take into account the higher transmission rates of these variants.