Norovirus vaccine pill protects against winter vomiting bug

A norovirus vaccine pill that cuts the risk of infection could be available in a few years, after it showed promise in a trial where people were intentionally exposed to the virus.

The highly contagious virus infects the stomach and intestines, causing vomiting and diarrhoea that typically resolve within a few days. “Billions are lost from the economy globally every year because of the lost days of work and hospitalisation,” says Sarah Caddy at Cornell University in Ithaca, New York.

Sean Tucker at biotech company Vaxart in San Francisco and his colleagues previously developed an oral vaccine that boosted levels of IgA antibodies that can block norovirus from entering cells, suggesting it could prevent infections.

Now, the researchers have tested this on 141 people aged between 18 and 49, about half of whom took the pill, while the others took a placebo. A month later, all the participants intentionally swallowed a high dose of the GI.1 strain of norovirus in liquid form, while in quarantine. “In the real-world setting, you need 10 to 100 viral particles to be infected, and we use 1 million particles,” says Tucker. This helped to ensure enough people got infected, he says.

In the following week, 82 per cent of those in the placebo group became infected, but only 57 per cent of vaccinated participants did.

“I think most individuals would be interested in taking [the vaccine] if you can reduce your risk by around [25 percentage points] and avoid getting really debilitating symptoms,” says Caddy, who wasn’t involved in the study.

The team also found that vaccinated participants shed substantially less virus in their stool and vomit than those who took the placebo. This suggests the vaccine could slow the spread of the virus, although that needs to be directly tested, says Caddy.

In another analysis, the scientists confirmed that the vaccine probably works by boosting levels of protective IgA antibodies in saliva and in the gut, blood and nose.

However, it is unclear how long this protection would last. Further work is also needed to verify the findings in young children and older adults, who are especially at risk of being hospitalised, says Caddy.

Most noroviruses that infect humans belong to two groups, known as GI and GII. Based on unpublished work by his team, the GI.1 vaccine would probably protect against other closely related GI variants, says Tucker. The team is also developing a vaccine that can protect against GI and GII viruses.

If all goes well, Tucker hopes the GI.1 vaccine could be rolled out in two to three years.