The FDA has lifted its clinical hold on a late-stage trial of Novavax's COVID-influenza and its standalone flu vaccines after a safety concern was found to be unrelated to the combination shot.

The Maryland-based biotech announced the clinical hold last month after a participant who had received its COVID-influenza combination vaccine had reported symptoms of motor neuropathy, or damage to the nerve cells that control muscles or movement.

The person was administered the vaccine in January last year as part of a mid-stage study. Novavax said it had changed the participant's symptoms to amytrophic lateral sclerosis, a condition that affects nerve cells in the brain and spinal cord, in additional details provided to the U.S. health regulator. 

Assessment showed the symptoms were not related to the shot, the company said. "The information provided to the FDA supported our assessment that the serious adverse event was not related to our vaccine," said Chief Medical Officer Robert Walker.

The company will resume late-stage trial activities as quickly as possible, he said.

Novavax's traditional protein-based COVID shot offers an alternative technology to messenger RNA-based rivals from Pfizer-BioNTech and Moderna but has failed to make a mark in the U.S. vaccine market.

Last year, the company had raised doubts about its ability to remain in business.