A Norovirus Vaccine May Be Coming

Norovirus is surging across the U.S., with case numbers higher now than they’ve been at the same time in more than a decade, according to the U.S. Centers for Disease Control and Prevention (CDC).

There is no antiviral treatment for the miserable but thankfully short-lived illness, and no vaccine—yet. But scientists at Moderna are in the late stages of testing what could be the first such shot, using mRNA technology against the virus. Here’s what to know about norovirus and where things stand with the development of a stomach-bug vaccine.

[time-brightcove not-tgx=”true”] Why norovirus is raging right now

“Commonly known as the stomach flu, norovirus has been around forever, and has become the leading cause of gastroenteritis or inflammation of the intestinal tract that causes vomiting and diarrhea,” says Dr. Edmund Milder, a pediatric infectious disease specialist at Rady Children’s Hospital and UC San Diego Health.

There are nearly 50 different subtypes, or genotypes, of norovirus, with different ones circulating in different years. For the last decade or so, one version of the virus, called GII.4, has been responsible for most infections around the world. That changed last year when GII.17 became the dominant strain. That could partially explain the current uptick in cases, since most people who have been exposed to other types of norovirus would not have as strong immunity to this version, making them more vulnerable to disease.

Norovirus symptoms

For most people, the infection causes intestinal symptoms such as vomiting, diarrhea, and dehydration. Unpleasant as they are, these symptoms don’t typically require medical care or hospitalization, and they tend to last just a few days. But older people and infants often experience worse disease, and each year in the U.S. about 100,000 people are hospitalized and nearly 1,000 people—mostly the elderly and the very young—die from the infection, mainly due to dehydration after not being able to keep down food and water, according to the CDC.

Is norovirus like other viruses?

No—for many reasons. First, it doesn’t take much of the virus to make someone sick. For most viruses, people would need to be infected with thousands of virus particles in order to feel ill, but it only takes as few as 10 to launch the intestinal symptoms typical of norovirus infection.

To make matters worse, the virus is encased in a particularly hardy cover that allows it to survive for days on surfaces like countertops and doorknobs. Hand sanitizer isn’t effective in killing norovirus—you’ll need to wash your hands for 20 seconds with soap and water to remove as much virus as possible—and the it also can’t be destroyed with high heat or cold temperatures. The most effective way to kill the virus on contaminated surfaces is by using a diluted solution of bleach and water, and allowing it to sit on a surface for at least five minutes before wiping.

Why isn’t there a norovirus shot yet?

The nearly 50 different versions of the virus mean that “each genotype requires a different immune response to provide protection,” says Dr. Doran Fink, therapeutic head of gastrointestinal pathogens and bacterial vaccines at Moderna. So any vaccine would have to be an educated guess as to which strains are likely to circulate in a given year—similar to the strategy behind updating the flu vaccine each season.

How close are we to having a norovirus vaccine?

Moderna is currently enrolling 25,000 people around the world in a phase 3 trial of the shot, after earlier testing showed encouraging results. In those studies, people vaccinated with the mRNA shot generated antibodies that in lab tests effectively blocked the norovirus protein in human gut cells; those given a placebo vaccine did not show the same antibody activity.

To improve the chances that the vaccine would be well-matched to circulating strains, Moderna’s vaccine candidate includes three different norovirus types. “It would be great if there were some conserved regions of the norovirus protein that could be targeted, but that’s not the case,” says Fink. Instead, their thinking goes, taking this multivalent approach should provide good protection against severe disease. It’s a strategy the company is also using on its multivalent mRNA flu vaccine. And the mRNA platform allows scientists to change and update viral targets more quickly, making it ideal for pivoting if viral strains change each season.

Targeting more than one viral protein has shown in the recent past to be effective: one of the mRNA COVID-19 shots was a bivalent vaccine that worked against two different strains of the virus.

Fink says Moderna expects to finish signing up volunteers in the spring, and plans to follow them for at least six months. But it may take longer to get a full report on how effective the vaccine is in the real world, since that would require having a certain number of people catch the virus to evaluate how they do. Testing the vaccine in different sites around the world should provide more data, however.

Would a vaccine stop me from getting norovirus?

Like the COVID-19 vaccine, the mRNA norovirus vaccine candidate is not designed to prevent people from getting infected. But it would theoretically help anyone immunized—especially the very young and elderly—from getting severely ill and being hospitalized.

How can I protect myself from norovirus?

Since there are no antiviral treatments or vaccines yet, the best way to avoid getting sick is by practicing good hygiene. Wash your hands often and avoid touching your face and mouth. If you do get sick, stay home to avoid infecting others, since you can still shed virus for anywhere from a few days to weeks after you feel better.