How close are we to a norovirus vaccine?

Norovirus, often erroneously called the "stomach flu," sickens an estimated 21 million Americans and 685 million people worldwide every year, and though there is currently no preventive vaccine, a promising contender is in the works.

The virus causes several nightmarish days of severe vomiting and diarrhea, often accompanied by fever, body aches and dehydration. The scourge is also maddeningly hardy and highly contagious. Although mortality rates are very low in developed countries, outbreaks can overwhelm emergency rooms, create unwelcome pressure on health care systems and cause widespread absences from work and school. It spreads particularly easily in close quarters, including daycares, cruise ships, universities and nursing homes.

Norovirus is not a form of influenza but rather a calicivirus. New strains appear every two to four years, and are "difficult to wipe out because they can withstand hot and cold temperatures as well as most disinfectants," said The Norovirus Foundation. Norovirus is "more a nauseating nuisance than a public-health crisis," said The Atlantic, but scientists have nevertheless been at work on a norovirus vaccine for years. In September 2024, the first volunteers were dosed in Moderna's advanced clinical trial for a norovirus vaccine that showed encouraging results in preliminary trials.

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What did the commentators say?

Experts have expressed caution about how feasible it will be to deliver a norovirus vaccine. "Will it work here? Keep a bucket handy, just in case," said the American Council on Science and Health in a post on X about the Moderna trial. That's because "norovirus has been devilishly difficult to even contemplate vaccinating against" given how rapidly it mutates, said the BBC. Rolling out an "effective, safe norovirus vaccine has been elusive, primarily because of the virus' high genetic diversity," and its large number of genotypes, said MedPage Today. Some skepticism also stems from the recent failure of a HilleVax vaccine for infants which "failed to meet key endpoints" in its trial in July 2024, said Clinical Trials Arena.

A recent winter surge of norovirus cases in the northern hemisphere, however, has renewed calls for vaccine development. "What better way to remind people of the power of vaccines than to eliminate the misery of puking?" said Alexandra Sifferlin at The New York Times. And while the "norovirus jab won't eliminate the bug, it could significantly reduce its impact on the health system," said The Independent.

What next?

Moderna researchers claim that "earlier trials of the vaccine have shown it generates a strong immune response in humans," and that the new trial is "designed to explore whether the jab is effective against the virus itself and, if so, how long protection lasts," said The Guardian. Moderna's norovirus inoculation uses the same mRNA technology that produced the company's revolutionary Covid-19 vaccines in 2020, which "use a genetic code to tell the body's cells to produce proteins that train the immune system," said Penn Medicine.

Moderna now needs to complete a "phase III trial," which is the final step before drugs or vaccines are submitted for the regulatory approval process in the United States. They are "critical to understanding whether vaccines are safe and effective," said Johns Hopkins University. Most phase III trials are randomized control trials, meaning that "participants and most of the study investigators do not know who has received the vaccine and who received the placebo," and are larger than earlier-phase trials, said Johns Hopkins.

In the Moderna norovirus trial, volunteers will participate for one year each, which will involve six in-person visits to trial sites as well as some monitoring and follow-up phone calls. The company hopes to enroll 25,000 people from all over the world, which will take two years. That means that even if the vaccine is shown to be safe and effective, it will not be available to the public until late 2026 or 2027. In the meantime, experts recommend washing your hands frequently, "especially after using the restroom, changing diapers and before preparing food or eating" and to avoid cooking food for others while sick, said The Mayo Clinic.