There is no approved vaccine for norovirus yet, but several companies are working on it.
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Emany yearssomewhere between 19 and 21 million Americans suffer from gastroenteritis (aka the “stomach flu”), most often caused by a group of pathogens called noroviruses. These infections lead to hundreds of thousands of hospital visits and hospitalizations, as well as approximately 900 deaths, each year. This winter, norovirus infections are particularly bad in the US, according to the CDC, which is recording its highest outbreak numbers in a decade.
There are two possible reasons for the current increase, said Daniel Kuritzkes, chief of infectious diseases at Harvard Medical School. Forbes. The first is that the types of circulating viruses change every year, which reduces immune defenses in a similar way to influenza and Covid. Additionally, people’s immunity to specific strains of norovirus wanes over time, making reinfection possible.
Much to the dismay 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, Kuritzkes notes, because the viral infection usually lasts only about a day or two, making it difficult to demonstrate a benefit to regulators. Additionally, the primary complication leading to hospitalization is dehydration, which is easily treated with IV fluids.
This makes a vaccine the most promising way to fight norovirus 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 first to market offers a huge opportunity, as annual virus infections cost the global economy around $60 billion, including both direct healthcare costs and indirect costs such as lost productivity. Moderna estimates that a norovirus vaccine has a total addressable market of about $3 billion to $5 billion.
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One of the main challenges of developing a norovirus vaccine, said Doran Fink, who leads Moderna’s development efforts, is that like the flu, there are dozens of strains that can be circulating at the same time, and these strains often have nothing in common. features that are recognized by the immune system. Immunity to one type will not necessarily protect you from another. That’s why Moderna’s vaccine currently targets three viruses at once, and it has another vaccine in early development that could target five. This is similar to seasonal flu vaccines, which are created anew each year to target multiple strains based on predictions of which ones are expected to circulate.
Something that makes this easier, Fink said, is that a particular type, called GII.4, has been responsible for most of the explosions for the past decade. By targeting GII.4 and two other circulating strains, he said, Moderna’s vaccine “may be able to cover over 70 or 80% of norovirus outbreaks that may occur in a given year. And with our mRNA technology, we will be able to update the vaccine composition in order to respond to the changes in which genotypes may circulate over time.
Another challenge for norovirus vaccines, Kuritzkes said, is that it attacks the body in the gastrointestinal tract, meaning a vaccine must promote enough neutralizing antibodies at that site to prevent infection. “Developing those types of vaccines has been scientifically challenging,” he said. However, it is not impossible, as the approved rotavirus and cholera vaccines attest.
Last summer, HilleVax, a company launched by Takeda Pharmaceuticals and Frazier Healthcare Partners to develop a norovirus vaccine, saw its stock 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, although it is still pursuing it for adults.
Targeting the gastrointestinal tract is one of the goals of another company, Vaxart, which is developing a norovirus vaccine that is taken as a pill rather than an injection. It is currently in the early stages of human testing of its vaccine, but Kuritzkes sees the approach as promising. “Like with typhoid and cholera, an oral vaccine makes a lot of sense because you’re trying to stimulate the immune response locally,” he said.
Fink acknowledged the challenges of antibodies entering the gastrointestinal tract and said the company is actively monitoring this as part of its development process. However, he noted that antibodies have been shown to migrate into the gastrointestinal tract in other experimental norovirus vaccines. Additionally, vaccines with similar technologies show that antibodies can migrate: For example, with Moderna’s Covid-19 vaccine, antibodies have been shown to move to the nasal mucosa (another site of norovirus infection).
Moderna dosed its first patient in a global phase 3 clinical trial (usually the last test before seeking regulatory approval) in September last year. Fink said the trial is expected to include about 25,000 patients and last about two years. Which means that even if there is a successful trial, it’s likely that its vaccine won’t be on the market until 2027 or later.
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 to protect yourself.”
