U.S. Food and Drug Administration staff said on Friday they were concerned about a possible risk of heart inflammation from Novavax Inc's vaccine, even as the company's data showed the vaccine was effective in reducing the risk of mild-to-severe COVID-19.
In the company's nearly 30,000 patient trial, conducted between December 2020 and September 2021, there were four cases of myocarditis, a type of heart inflammation also associated with mRNA vaccines, detected within 20 days post vaccination.
One patient in the trial reported myocarditis after receiving placebo.
"These events raise the concern for a causal association with this vaccine, similar to the association documented with mRNA COVID19 vaccines," the FDA staff wrote in briefing documents released on Friday.
Shares of the company fell nearly 14% after the FDA's analysis of data from the company's trial.
The FDA said it had requested Novavax to flag myocarditis and another kind of heart inflammation called pericarditis as an "important identified risk" in its materials. The company had not yet agreed to do so.
Novavax said the number of myocarditis events in its clinical trial was "within the range of expected background cases."
Novavax has said its protein-based shot will play a role in driving vaccination among those who have been hesitant to get immunized and it has started an educational effort on vaccine choices.
"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," it said.
The FDA analyzed data from Novavax's trial before the Omicron and Delta variant became the dominant 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," the FDA staff said.
The comments came in a briefing note initially prepared ahead of a May 7 meeting of the FDA's outside advisers. The FDA staff comments will be used by those advisers to guide their decision on whether or not to recommend authorizing the vaccine on Tuesday. The FDA is not mandated to follow the advise of its outside experts, but usually does.
In the company's study, which enrolled about 30,000 adults in the United States and Mexico, the vaccine had an efficacy of 90.4%.
(Reporting by Manas Mishra and Mrinalika Roy in Bengaluru, and Michael Erman in New Jersey; Editing by Saumyadeb Chakrabarty and David Holmes)