(Reuters) -Vaccine maker Novavax's ( NVAX ) shares plunged over 22% on Thursday after Health and Human Services Secretary Robert F. Kennedy Jr. raised concerns about the company's COVID-19 vaccine in an interview with CBS News.

The U.S. Food and Drug Administration, an agency that is part of the U.S. Department of Health and Human Services, missed its deadline last week for deciding on the traditional approval of the vaccine. The vaccine has been sold under an emergency use authorization since 2022.

When asked if the delay resulted from "personnel being shuffled" at the FDA, Kennedy attributed it to the vaccine's composition. He said Novavax's ( NVAX ) single antigen approach "has never worked" for respiratory illnesses.

The Maryland-based company's protein-based COVID-19 vaccine, offers an alternative to the mRNA-based technologies of competitors Pfizer ( PFE ) and Moderna ( MRNA ).

Novavax ( NVAX ) said on Thursday it continues to believe its application included data that showed the shot was safe and effective in preventing COVID-19, and that it has not received an official response from the agency regarding the status of the application.

Last week, Novavax ( NVAX ) told Reuters that the company had responded to the FDA's information requests by April 1 and said its application is "ready for approval."

Kennedy, who has expressed skepticism about vaccine safety and efficacy for years, initially hit biotech and vaccine company shares in February after he was confirmed by the Senate to the position.

The sector has also been under pressure following 10,000 layoffs undertaken by the Trump administration at health agencies, including the FDA.