Despite millions of cases of norovirus in the U.S

How Much Longer Do We Have to Wait for a Norovirus Vaccine? each year—and a current surge in outbreaks—there is still no vaccine for the stomach bug. Here's why it's taking so long, and how close we are to a norovirus vaccine

Despite millions of cases of norovirus in the U.S

• There is currently no vaccine for norovirus because of its many strains and the elusive nature of how the virus evolves.
• The closest norovirus vaccine is a Moderna trial wrapping up in 2027, but it could still be years after the trial ends before the vaccine is approved for the public.
• In the meantime, experts say the best way to protect against norovirus is practicing basic hygiene habits, like washing your hands.

Dozens of norovirus outbreaks have been reported across the country in recent weeks. And as people grapple with the vomiting, diarrhea, and other potentially dangerous symptoms associated with the virus, many are left wondering why there’s no vaccine to protect against these common infections.

The Centers for Disease Control and Prevention (CDC) reported 91 confirmed norovirus outbreaks for the week of Dec. 5, up from the 41 outbreaks reported that same week in 2023.

Plus, since mid-December, the Food and Drug Administration (FDA) has issued four separate recalls warning consumers that certain oysters and clams may be contaminated with norovirus. Anecdotally, people say the virus is surging.

There are, on average, between 19 and 21 million norovirus cases annually in the U.S., which lead to over 100,000 hospitalizations. Most of these severe cases occur in young children or older adults. Globally, 200,000 people die of norovirus each year, including about 900 people in the U.S. It’s estimated that the virus costs the U.S. $2 billion annually.

But despite norovirus’ prevalence, there are few preventative tools available to stop transmission or block severe disease. Multiple pharmaceutical companies are working on a norovirus vaccine; however, experts said they likely won’t be available anytime soon.

There are a number of hurdles standing in the way of these shots, said Mark Cameron, PhD, associate professor in the Department of Population and Quantitative Health Sciences at the Case Western Reserve University School of Medicine.

“Norovirus is one of those stubborn, highly contagious, moving target viruses with complex genetic evolution that spawns—and will continue to spawn—a lot of variants,” Cameron told Health. "But there are other reasons a norovirus vaccine isn’t commercially available yet, including [the fact that] there isn’t a solid preclinical model to affordably test whether a particular vaccine candidate is on the right track."

Here’s what experts had to say about why developing a norovirus vaccine has been so difficult, how long it could take until one hits the market and ways to protect yourself in the meantime.

Why Don’t We Have a Norovirus Vaccine Yet?

The creation of a norovirus shot has been particularly elusive in large part due to how the virus evolves, experts said.

“It really is evolving extremely rapidly, and that’s a big problem,” Patricia Foster, PhD, professor emerita of biology at Indiana University, Bloomington, told Health.

There are also dozens of different subtypes of norovirus and multiple dominant types that frequently cause outbreaks. This explains why people can get repeat norovirus infections throughout their lives. Hypothetically, even if someone were to develop immunity to one strain of norovirus—whether through an infection or a vaccine—they could still get sick with another.

Multiple Vaccines Are in the Works

Despite these challenges, researchers are working on vaccines. And progress is moving at a quicker pace thanks in part to new technologies developed in the last decade.

In 2016, Baylor College of Medicine researcher Mary Estes, PhD, and her colleagues developed a method to cultivate norovirus outside of the human body, allowing scientists to test different pathways for vaccines and treatments. This is especially important since mice—frequently used in animal studies—don’t usually get sick from human norovirus.

Now, researchers can investigate experimental vaccines, including a 2023 shot created by researchers at the Washington University School of Medicine in St. Louis, which adds norovirus to an existing vaccine for rotavirus, another diarrhea-causing bug.

Plus, a number of pharmaceutical companies are working on vaccine candidates, too. Many are currently in clinical trials, Amesh Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, told Health.

HilleVax, a Boston-based pharmaceutical company, has been testing a norovirus vaccine from the Japanese company Takeda. However, that vaccine failed a phase II clinical trial in June 2024. A norovirus vaccine tablet produced by San Francisco-based biotechnology company Vaxart recently completed phase I clinical testing.

Most promising is the vaccine candidate from Moderna, which is currently being tested in human participants.

“Moderna just started a phase III clinical trial of an mRNA-based vaccine for norovirus that will wrap up in 2027,” Cameron said. “Since mRNA vaccines can pack more proteins into [their] unique designs—three in this case for multiple norovirus genotypes—we might just be on the precipice of a commercial norovirus vaccine as the trial plays out.”

That said, the Moderna vaccine may not solve all problems created by norovirus.

“It’s probably wrong to think of the Moderna norovirus vaccine as a ‘universal’ vaccine that will stop norovirus permanently in its tracks,” Cameron explained. “But the design hedges those bets and can be modified to keep ahead of the emergence of norovirus variants, akin to current COVID-19 and flu vaccine programs.”

In other words, an annual norovirus vaccine designed to protect against circulating strains may be on the horizon.

But before the vaccine becomes available to the public, it’ll have some regulatory hurdles to clear; the next step—should the results be favorable—would be for Moderna to request approval for the vaccine from the FDA, which would then review the available data before making a decision.

Preventing Norovirus, Even Without a Vaccine

Norovirus is incredibly contagious and can be quite difficult to contain once somebody gets sick. This has to do with the structure of the virus itself.

“Viruses all have different structures, and some of them have kind of a fatty envelope around them that helps them infect your cells,” said Adalja. These so-called enveloped viruses are relatively easy to kill with soap and alcohol-based cleaners, he explained.

However, norovirus is a nonenveloped virus, like polio and many other gastrointestinal illnesses. These viruses are hardier and can remain on surfaces for days or even weeks. They’re also “more resistant to deactivation with soap and water,” said Adalja.

Because of this, neither hand sanitizer nor soap and water actually kill norovirus, Foster explained. “Washing your hands works because you’re washing off [the virus],” she said.

This means that these basic hygiene habits such as hand washing are really among the only protections we have against norovirus, Ming Tan, PhD, infectious disease researcher and associate professor of pediatrics at Cincinnati Children’s Hospital Medical Center, told Health.

“Wash your hands before you eat and after you go to the restroom,” he said. “That’s the standard hygiene procedure to reduce the risk of infection.”

But, according to the CDC, thoroughly cooking shellfish, washing your produce before eating it, cleaning any contaminated surfaces, and washing your laundry in hot water can also help lower your chances of getting sick.

If you do get norovirus, there’s little to be done in terms of treatment, Tan said. Drinking fluids while you’re ill can prevent further complications from dehydration. And some people may benefit from medications that reduce diarrhea or nausea—these can be available over-the-counter or via a prescription, such as Zofran.

However, these drugs aren’t necessary to help you heal, experts said. Most people recover from norovirus in one to three days.

If you or someone in your family develop symptoms of severe disease, such as altered mental state, high fever, or severe pain in the abdomen, seek care immediately.

Julia is a news reporter and editor for Health, where she covers breaking and trending news on health and wellness topics. Her work has been featured in The Heights, an independent student newspaper at Boston College, and Minnesota Monthly.

This story originally appeared on: Health News - Author:Maggie O'Neill