The U.S. Food and Drug Administration has put Novavax's trial of an experimental COVID-flu vaccine combination on hold after one person who received the shot reported nerve damage, the company said on Wednesday.

Shares of the vaccine maker plunged more than 24% to $9.48 in premarket trading. Novavax said it was working with the FDA to resolve the clinical hold on the trial of its combination shot and the standalone flu vaccine.

A participant enrolled in a mid-stage study of the vaccine reported symptoms of motor neuropathy, or damage to the nerve cells that control muscles or movement, last month.

The company said other trials of COVID-19 and flu vaccines had not shown any safety signal for motor neuropathy. It did not believe that it was established that the vaccine had caused the safety event, but was working to provide more information to the FDA.

"Our goal is to successfully resolve this matter and to start our Phase 3 trial as soon as possible," said Robert Walker, the company's chief medical officer.

Novavax's protein-based COVID vaccine is the biotech's only commercial product. The shot has failed to make a significant dent in the market share of early COVID-vaccine entrants such as Pfizer/BioNTech and Moderna.

In May, Novavax signed a licensing deal worth at least $1.2 billion with Sanofi, giving the U.S biotech firm much-needed liquidity. It also provided the French drugmaker a license to co-sell Novavax's vaccine in most countries and use the COVID shot along with its own flu vaccines to develop a combination shot.