The mRNA vaccines' early success "gives us some encouragement for the technology for other vaccine targets in the future," said Dr. Mark Mulligan, director of the Vaccine Center at NYU Langone Health.

Moderna is testing several preventive mRNA vaccines in human studies, including one against cytomegalovirus, a common virus that can cause health problems in babies whose mothers caught it during pregnancy. The vaccine was generally safe and induced the desired immune responses in early studies. Testing continues.

Moderna is also testing with Merck whether an mRNA-based therapeutic vaccine can treat cancer. The treatment is custom-made for each patient based on mutations found in their tumor cells. The shot, when given with Merck's cancer drug Keytruda, showed promise in some patients with head and neck cancer in a small, early-stage study, Moderna said this month.

BioNTech continues advancing potential mRNA vaccines to treat cancer, including tumors for breast, skin and the pancreas. The company has several cancer shots in development, including one for a type of skin cancer in mid-stage testing.

One of the advantages of mRNA vaccines, Dr. Sahin said, is that they can be quickly adjusted so vaccines can better respond to an eventual decline in immunity or virus mutations, which could render other vaccines less effective.

Dr. Sahin said that regulator authorization could potentially lead to a "whole new category of medicines."

Write to Peter Loftus at peter.loftus@wsj.com, Jared S. Hopkins at jared.hopkins@wsj.com and Bojan Pancevski at bojan.pancevski@wsj.com

(END) Dow Jones Newswires

11-17-20 1403ET