A norovirus vaccine could be on the horizon as cases rise

Norovirus is raging across the U.S. this winter. Moderna might soon have a vaccine for it. 

A large phase three trial of the shot is underway, with results expected as soon as later this year or 2026. Moderna needs to see a certain number of cases before it can analyze the data and determine how well its vaccine works, putting the timeline in flux. The 25,000-person study is enrolling ahead of schedule, said Doran Fink, Moderna’s clinical therapeutic area head for gastrointestinal and bacterial pathogens. 

“I don’t know if it’s directly attributable to the increased incidence of norovirus this season, but we clearly have a lot of interest in participation in this trial,” Fink said. 

Norovirus is a nasty stomach bug that causes vomiting and diarrhea. It’s highly contagious and can spread easily in nursing homes and daycares, and on cruise ships. It’s generally a seasonal illness that’s more common in the winter months. 

This winter has been especially brutal. Twice as many norovirus tests are coming back positive this January than the same time last year, according to data from the Centers for Disease Control and Prevention. Norovirus outbreaks were up 36% so far this season as of Dec. 11, according to the CDC. 

There’s currently no vaccine for norovirus. Like flu, there are many types of norovirus, making immunizing against it a challenge.

Moderna’s vaccine candidate targets the three genotypes that the company says typically cause most infections. It works by showing the immune system something that looks like norovirus but isn’t infectious, so the body can learn how to fight back if the real thing hits.

The company’s vaccine candidate does not include the genotype that’s causing the bulk of this year’s infections. One of the study’s goals is to see whether the vaccine protects against more types of norovirus than the shot specifically targets, Fink said. He said mRNA vaccines offer an advantage because they can easily be tweaked, if needed. 

Moderna’s goal isn’t to prevent people from getting norovirus entirely. That’s a high bar for any vaccine, and one that’s especially difficult to achieve with norovirus because the symptoms start within 12 to 24 hours of exposure, Fink said. Instead, the goal is to make people feel a little less awful and keep them from needing to see a doctor or go to the hospital if they do get it. 

The company sees the main opportunity in vaccinating seniors who are particularly vulnerable to norovirus complications like dehydration. People 65 and up make up the majority of the estimated 900 Americans who die from norovirus complications in the U.S., according to the CDC. 

Moderna also sees health-care workers, daycare workers and other teachers who are exposed to young children as possible target populations, Moderna Chief Executive Officer Stephane Bancel said last week at the JP Morgan Health Care Conference. People going on cruises is another possibility, he said, since the virus can spread easily on ships where people are living in tight quarters. 

Investors are questioning whether Moderna can make the shot a commercially viable opportunity – if, of course, the vaccine works, said RBC analyst Luca Issi. He sees the shot being used mostly to protect people living in nursing homes or going on cruises. 

At this point, Moderna isn’t testing the vaccine in children, who are also vulnerable to norovirus. But if the shot works in adults, Moderna would be obligated to study it in children, Doran said.