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Why is there no stomach flu-norovirus vaccine?

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Why is there no stomach flu-norovirus vaccine?

Eall yearSomewhere between 19 and 21 million Americans suffer from gastroenteritis (also called “stomach flu”), usually caused by a group of pathogens called noroviruses. These infections lead to hundreds of thousands of emergency room visits and hospitalizations each year, as well as approximately 900 deaths. Norovirus infections are particularly severe in the US this winter, according to the CDC with the highest outbreak rates of the past decade.

There are two possible reasons for the current increase, says Daniel Kuritzkes, chief of infectious diseases at Harvard Medical School Forbes. The first is that the circulating viruses change every year, reducing immune protection in the same way as with flu and Covid. In addition, people’s immunity to certain strains of norovirus wanes over time, making reinfections possible.

Much to the dismay of parents, teachers and cruise ship enthusiasts, no approved treatments for norovirus infections exist, nor is there a vaccine against it. It’s unlikely that a treatment for norovirus will be developed, Kuritzkes notes, because the viral infection typically lasts only about a day or two, making it difficult to demonstrate a benefit to regulators. Additionally, the main complication leading to hospitalizations is dehydration, which is easily treated with IV fluids.

This makes a vaccine the most promising way to combat noroviruses at the moment. There are three vaccine candidates currently moving through the clinical pipeline into human trials, and the furthest along is Moderna, which has developed a norovirus vaccine using the same mRNA technology as that used for Covid-19. Being first to market offers great opportunity, as annual infections of the virus cost the global economy approximately $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 to $5 billion.


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One of the key challenges in developing a vaccine against norovirus, says Doran Fink, who leads Moderna’s development efforts, is that, like the flu, there are dozens of strains circulating at once, and these strains often have no commonality. have characteristics. characteristics recognized by the immune system. Immunity to one species does not necessarily protect you against another species. 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 viruses. This is similar to seasonal flu vaccines, which are regenerated each year to target multiple strains based on predictions they are expected to be in circulation.

Something that makes this easier, Fink says, is that a particular strain called GII.4 has been responsible for the majority of outbreaks over the past decade. By targeting GII.4 and two other circulating strains, he said, Moderna’s vaccine could “cover more than 70 to 80% of the norovirus outbreaks that might occur in a given year. And with our mRNA technology, we could update the vaccine composition to respond to 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 location to prevent infection. “Developing these types of vaccines has been a scientific challenge,” he said. However, this is not impossible, as shown by approved vaccines against rotavirus and cholera.

Last summer, HilleVax, a company launched by Takeda Pharmaceuticals and Frazier Healthcare Partners to develop a norovirus vaccine, saw its stock price plummeted last July when it reported that its vaccine candidate was found to be ineffective in preventing infections in infants. The company said it is halting development of the vaccine for infants, although it is still developing 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. The company is currently in the early stages of testing its vaccine in humans, 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 on the spot,” he said.

Fink acknowledged the challenges of reaching antibodies in the gastrointestinal tract and said the company is actively monitoring this as part of its development process. However, he noted that in other experimental norovirus vaccines, antibodies have been shown to migrate to the gastrointestinal tract. Furthermore, vaccines with similar technology show that antibodies can migrate: for example, Moderna’s Covid-19 vaccine shows that antibodies move to infection sites in the nose.

Moderna has dosed its first patient in a global Phase 3 clinical trial (usually the last test before seeking regulatory approval) in September from last year. Fink said the testing is expected to include about 25,000 patients and last about two years. That means that even if there is a successful trial, it likely won’t be until 2027 or later before the vaccine hits the market.

Until then, Kuritzkes said it’s important to remember that noroviruses, unlike respiratory viruses, are “incredibly hardy” and can survive on surfaces and can even withstand hand sanitizer. The best defense against this, he added, is to “wash your hands with soap and water,” he added. “Personal hygiene is the most important thing if you want to protect yourself.”

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