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Moderna May Have The Best Shot At A Vaccine For Stomach Flu

There's no approved norovirus vaccine yet, but several companies are working on it.

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Every year, somewhere between 19 and 21 million Americans come down with gastroenteritis (aka "stomach flu"), most often caused by a group of pathogens called noroviruses. These infections lead to hundreds of thousands of ER visits and hospitalizations, as well as around 900 deaths, every year. This winter, norovirus infections are particularly bad in the U.S., according to the CDC, which is recording the highest outbreak numbers of the last decade.

There are two possible reasons for the current surge, Daniel Kuritzkes, chief of infectious diseases at Harvard Medical School told Forbes. The first is that strains of circulating viruses change each year, which reduces immune protections similarly to influenza and Covid. Additionally, people's immunity to particular strains of norovirus wane over time, making reinfections possible.

Much to the consternation of parents, teachers and cruise ship enthusiasts, there are no approved treatments for norovirus infections, nor is there any vaccine against it. A treatment for norovirus is unlikely to be developed, notes Kuritzkes, because the viral infection typically lasts just about a day or two, making it hard to demonstrate a benefit to regulators. Additionally, the primary complication that leads to hospitalizations is dehydration, which is easily treated with IV fluids.

This makes a vaccine the most promising avenue for fighting noroviruses right now. There are currently three vaccine candidates moving through the clinical pipeline in human trials right now, and the furthest along is Moderna, which has developed a norovirus vaccine with the same mRNA technology as the one for Covid-19. Being the first to market provides a big opportunity, given that annual infections of the virus cost the global economy around $60 billion, including both direct healthcare costs as well as indirect costs such as productivity losses. Moderna estimates that a norovirus vaccine has a total addressable market of about $3 to $5 billion.

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One of the main challenges of developing a vaccine against norovirus, said Doran Fink, who leads Moderna's development efforts, is that like the flu, there are dozens of strains that might be circulating at one time, and these strains often don't have common features that are recognized by the immune system. Immunity to one strain won't necessarily protect you from another. That's why Moderna's vaccine currently targets three viruses at once, and it has another vaccine in earlier stages of development that can target five. This is similar to seasonal flu vaccines, which are newly generated each year to target multiple strains based on forecasts of which are expected to be circulating

Something that makes this easier, said Fink, is that one particular strain, called GII.4, has been responsible for a majority of outbreaks for the past decade. By targeting GII.4 and two other circulating strains, he said, Moderna's vaccine "could be able to cover upwards of 70 or 80% of the norovirus outbreaks that might occur in a given year. And with our mRNA technology, we would be able to update the vaccine composition in order to respond to changes in which genotypes might circulate over time."

Another challenge for norovirus vaccines, said Kuritzkes, is that it attacks the body in the gastrointestinal tract, which means a vaccine needs to promote enough neutralizing antibodies at that location to prevent infection. "Developing those kinds of vaccines has been scientifically challenging," he said. It's not impossible, though, as approved vaccines for rotavirus and cholera attest.

Last summer, HilleVax, a company launched by Takeda Pharmaceuticals and Frazier Healthcare Partners to develop a norovirus vaccine, saw its share price plummet last July when it reported that its vaccine candidate proved ineffective at preventing infections in infants. The company said it was halting development of the vaccine for infants, though it's still pursuing it for adults.

Targeting the GI tract is one of the goals of another company, Vaxart, which is developing a norovirus vaccine that's taken as a pill, rather than an injection. It's currently in early stage human testing of its vaccine, but Kuritzkes sees the approach as promising. "As with typhoid and cholera, an oral vaccine makes a lot of sense because you're trying to stimulate the immune response at the site," he said.

Fink acknowledged the challenges of antibodies getting to the GI tract and said the company's actively monitoring that as part of its development process. However, he noted that antibodies are shown to migrate to the GI tract in other experimental norovirus vaccines. Additionally, vaccines with similar technology show that antibodies can migrate: For instance, with Moderna's Covid-19 vaccine, antibodies are shown to move to sites of infection in the nose.

Moderna dosed its first patient in a global phase 3 clinical trial (usually the last test before seeking regulatory approval) in September of last year. Fink said that testing is expected to include around 25,000 patients and will take about two years. Which means that even if there's a successful trial, it likely wouldn't be until 2027 or later that its vaccine hits the market.

Until then, Kuritzkes said it's important to remember that unlike respiratory viruses, noroviruses are "incredibly hardy" and can survive on surfaces and even withstand hand sanitizer. The best defense against it, he added, is "washing your hands with soap and water," he added. "Personal hygiene is the most important thing in protecting yourself."

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Flu, Contagious Viruses Surging In Schuylkill County, Doctors Say

Cases of influenza, other contagious respiratory ailments and norovirus are surging in the Schuylkill County region, area health officials say.

There have been more cases of flu, RSV and norovirus in the region so far this season than at any point since prior the COVID-19 pandemic of 2020, said infectious disease specialist Dr. Jeffrey A. Jahre for St. Luke's University Health Network.

Dr. Kendall Melewsky counts tablets of amoxicillin and clavulanate potassium at Towne Drugs in Pottsville, Wednesday, Jan. 15, 2025. (MATTHEW PERSCHALL/MULTIMEDIA EDITOR)

We are now in the midst of respiratory illness season, and COVID-19 cases also are higher than in the past two years, Jahre said.

"It's a very notable year," he said.

Other local doctors agreed that viral cases are up, basing that on statewide data, anecdotal evidence and the number of patients coming to area hospital networks and being admitted due to those conditions.

It is normal for there to be a rise in flu, COVID and RSV around the state and country this time of year as people are indoors more often, according to the federal Centers for Disease Control and Prevention.

Dr. Kendall Melewsky counts tablets of amoxicillin and clavulanate potassium at Towne Drugs in Pottsville, Wednesday, Jan. 15, 2025. (MATTHEW PERSCHALL/MULTIMEDIA EDITOR)

But the numbers being higher this season than in recent years is due in part to fewer people getting vaccinated against those illnesses because of what Jahre called "vaccine fatigue."

There has been so much information spread about vaccines — much of which Jahre calls false or conflicting — that many people have stopped getting annual vaccines altogether, he said.

"People don't know what to believe, and they're saying, 'I'm done with vaccines,' " he said. "That is a huge mistake. Prevention is better than cure."

As a result, many are getting those viruses they otherwise could have been protected from or are getting sicker than they would have if they'd been vaccinated, he said. That is especially dangerous for those at high-risk for viral complications, or those who come in contact with high-risk people, he said.

Because respiratory virus cases have been down the last few years, partly because many also took precautions such as working from home and masking, fewer people have residual immunity from those illnesses, which has also helped cause the recent surge, including among young children, Jahre said.

"Pediatric hospitals are full from here to Philadelphia," he said.

Norovirus, which causes gastrointestinal symptoms, does not have a vaccine and does not provide residual immunity, meaning you can get it repeatedly, and St. Luke's has also seen a spike in cases of that virus recently, he said.

For some, norovirus causes several bad days of nausea, vomiting and diarrhea followed by a period of fatigue, but for those at risk it can lead to hospitalization due to dehydration, he said.

Respiratory virus season started on Sept. 29, according to the state Department of Health, and on Jan. 11 when the most recent data was released, 598 laboratory-confirmed flu cases had been reported in Schuylkill County. Over the same period, 510 laboratory-confirmed RSV cases were reported in the county.

Mandatory reporting requirements for COVID ended in Pennsylvania when the national Public Health Emergency concluded in 2023.So no data is available on cases or specific to counties, but statewide there have been 470 COVID deaths reported among Pennsylvania residents by the National Center for Health Statistics during the 2024-25 season.

Geisinger Health System also has seen a rise in viral illnesses, including flu, RSV, COVID and norovirus, over the past few weeks, said Dr. Stanley Martin, infectious disease specialist.

Most of those who have come to Geisinger's offices or emergency rooms in central Pennsylvania with those ailments were able to be treated and given a recommendation for over-the-counter or prescription medicines to reduce their symptoms. But some people have required hospitalizations, he said.

The people hardest hit by respiratory or gastrointestinal viruses are usually those 65 and older; those 5 years old and younger; or those who have compromised immune systems or serious underlying health problems, he said.

Martin recommended that people who have not yet had flu shots this season get one now, and that they plan on getting vaccinated against influenza and COVID every fall. While those vaccines don't guarantee you won't get sick, they are the best way to lower that risk, he said.

"Some protection is better than no protection," he said.

It's hard to come up with exact case numbers on the viruses because many don't go to their doctor or hospital or get tested, and the symptoms of the respiratory illnesses are similar to one another, he said.

It's clear, though, that respiratory virus and norovirus cases have also been high recently at Lehigh Valley Hospital – Schuylkill in Pottsville, said Dr. Maksim Lapkovsky, who works in the emergency room.

"We are smack in the middle of flu season, and it seems to be a pretty bad one," he said, both in terms of case numbers and how severely the virus is hitting some people.

Most can treat the symptoms with over-the-counter medicine, will feel lousy for a week and then return to normal, Lapkovsky said.

But those with conditions like COPD or asthma should be careful it does not lead to a lung infection and should be quicker to seek medical help, he said.

Lapovsky agreed that it is the worst flu season locally since prior to 2020, with almost half of recent ER patients testing positive.

"We're back to pre-COVID (pandemic) levels of the flu," he said.

The health department recommends that Pennsylvanians stay updated with COVID, flu and RSV vaccinations and continue fundamental health and hygiene practices, like handwashing, staying home when sick and avoiding contact with people who have suspected or confirmed respiratory illness.

While norovirus, sometimes called the "stomach flu" or "stomach bug," can occur at any time of the year, it is most common between November and April, doctors said. The virus is very contagious and can spread quickly from person to person through close contact with someone who has the virus, touching contaminated surfaces and then touching your mouth or nose, and eating or drinking contaminated foods or beverages.

Additionally, children younger than 5, older adults, and people with weakened immune systems are more likely to develop severe norovirus infections.

Pennsylvanians can also decrease their chances of coming in contact with noroviruses by carefully washing fruits and vegetables, cleaning any contaminated surfaces immediately after an episode of illness by using a bleach-based household cleaner and immediately removing and washing clothing or linens that may be contaminated with virus after an illness.

Those infected with norovirus should not prepare food while they have symptoms or for three days after they recover from their illness. Food that may have been contaminated by an ill person should be disposed of properly.

Flu Symptoms To Watch Out For As Winter Illnesses Surge

As we slowly trudge through winter, respiratory illnesses like COVID-19 and the flu are surging across the country.

For the week ending January 4, 18.6 percent of influenza tests came back positive, with influenza A(H1N1)pdm09 and A(H3N2) the most predominant variants during this period, according to the U.S. Centers for Disease Control and Prevention (CDC).

"Nationally, emergency department visits are high for diagnosed influenza," the CDC said. "Five influenza-associated deaths occurring during the 2024-2025 season were reported this week for a total of 16 deaths this season."

A stock image shows a woman with the flu, along with viruses in the inset image. Flu symptoms can include fevers, coughs, headaches and body chills. A stock image shows a woman with the flu, along with viruses in the inset image. Flu symptoms can include fevers, coughs, headaches and body chills. ISTOCK / GETTY IMAGES PLUS

The flu, or influenza, is a contagious respiratory illness caused by viruses and primarily affects the nose, throat and lungs. It is spread via respiratory droplets, which are emitted when an infected person coughs, sneezes or talks.

What Are the Symptoms of Flu?

Symptoms usually come on suddenly, according to the CDC, and can include fevers above 100.4 degrees F, dry cough, sore throat, runny nose, body aches, headaches, chills and occasionally nausea, vomiting or diarrhea.

Symptoms may be more severe for people over 65 or younger than 5, pregnant women and those with certain chronic medical conditions, such as asthma, diabetes or heart disease.

"Some people will develop complications (such as pneumonia) as a result of flu, some of which can be life-threatening and result in death," the CDC said. "Other possible serious complications triggered by flu can include inflammation of the heart (myocarditis), brain (encephalitis) or muscle tissues (myositis, rhabdomyolysis), and multi-organ failure (for example, respiratory and kidney failure)."

COVID-19 symptoms and flu symptoms are very similar, insofar as they cannot be diagnosed by symptoms alone, with testing required to distinguish one from the other.

"Compared with flu, COVID-19 can cause more severe illness in some people. Compared to people infected with influenza virus, people infected with SARS-CoV-2 may take longer to show symptoms and may be contagious for longer periods of time," the CDC said.

Can You Have the Flu Without a Fever?

While fever is a common symptom of the flu, not everyone with the virus will develop one. If the infection is mild, the body might not generate a fever, but people with weakened immune systems or older people may not experience fever because of their lessened immune response.

How Long Does It Take to Recover From the Flu?

Recovery from the flu typically takes one to two weeks, but the timeline can vary depending on factors like age, overall health and the severity of the infection. Children and older adults may take longer to recover, and conditions like asthma, diabetes or heart disease can prolong recovery.

What Is the Difference Between Flu A and B?

Influenza A and B are two types of influenza viruses that cause seasonal flu outbreaks. Flu A is found in humans, birds, pigs and other animals, and its subtypes are based on its surface proteins: hemagglutinin (H) and neuraminidase (N) (for example, H1N1, H3N2).

Flu B, on the other hand, is found only in humans (and occasionally in seals). Flu A is more widespread and often the dominant strain during flu season. Flu B generally causes milder illness compared with flu A, but severe cases can still occur.

"Of the 1,783 viruses reported by public health laboratories, 1,743 were influenza A and 40 were influenza B," the CDC said.

Is It Too Late to Get a Flu Shot?

The flu season runs between October and May in most regions, peaking between December and February. While getting vaccinated earlier is ideal for maximum protection, getting the vaccine later can still be beneficial, especially if flu activity is ongoing in your area.

The vaccine takes approximately two weeks to reach full immunity, so getting it now can still protect you during the active part of the flu season. Even if you're exposed to the flu virus before full immunity develops, the vaccine can reduce the severity of illness and lower the risk of complications like pneumonia or hospitalization.

"CDC recommends that everyone ages 6 months and older get an annual influenza (flu) vaccine," the CDC said.

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