Despite evidence that Novavax Inc’s COVID-19 vaccine may reduce the risk of mild to severe infections, the US Food and Drug Administration (FDA) has raised concerns about the vaccine’s potential to cause heart inflammation.

In Novavax’s nearly 30,000 patient studies, which took place between December 2020 and September 2021, four cases of myocarditis were discovered within 20 days of getting the protein-based shot.

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Following the FDA’s data evaluation of the company’s trial, its stock fell roughly 14%.

The FDA mentioned that it had asked Novavax to mark myocarditis and another type of heart inflammation known as pericarditis as an “important identified risk” in its data. Novavax has not agreed to this yet.

In response to the FDA’s safety concerns, Novavax stated that naturally occurring myocarditis can be expected in any sufficiently large database.

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“Based on our interpretation of all the clinical data supporting NVX-CoV2373 … we believe there is insufficient evidence to establish a causal relationship,” Reuters quoted the company as saying.

One patient in the study developed myocarditis after receiving a placebo.

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According to Novavax, NVX-CoV2373 will help promote vaccination among those who have been apprehensive to get immunised, and the company has started an awareness programme on vaccine options.

The FDA examined data from Novavax’s experiment before the Omicron and Delta variants became the most common strains.

“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,” Reuters quoted FDA staff as saying.

The vaccine had a 90.4 % efficacy rate in Novavax’s study, which included people from all over the United States and Mexico.

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The FDA’s comments were shown in a briefing note primed ahead of the agency’s outside advisers meeting on May 7.

On Tuesday, outside advisors will use the comments of FDA staff to help them decide whether to recommend authorising the use of the vaccine.