An artist’s impression of the norovirus
Science Photo Library/Alamy
An early trial of a norovirus vaccine pill has shown promise at protecting against the notorious “winter vomiting” bug, with researchers saying it could potentially be available for use in a few years.
The virus is highly contagious, infecting the stomach and intestines and causing vomiting and diarrhoea. Most people recover within a few days, but very young and older people are especially at risk of ending up in hospital, with significant healthcare costs. “Just in the US alone, it’s a 10 billion-[dollar]-a-year problem,” says Sean Tucker at biotech company Vaxart in San Francisco, California.
This has spurred scientists to develop a vaccine, but so far, efforts have failed. That is partly because prior attempts have focused on developing injectable vaccines, which are less good at generating protective antibodies in the intestine, where the virus replicates, says Tucker.
To address this, Tucker and his colleagues previously developed an oral norovirus vaccine that delivers a protein from the GI.1 norovirus variant into the intestine. An initial trial in adults under 50 found that the pill could generate norovirus-specific antibodies in their guts, but people in this age group probably wouldn’t be a priority for a vaccine given that they generally recover from the virus easily.
Now, the researchers have tested the vaccine in people in the US aged between 55 and 80. The team gave 11 of them the pill while 22 others took a placebo. About a month later, the researchers collected blood and saliva samples from the participants.
They found the people who took the vaccine had higher levels of IgA antibodies, which can block norovirus from entering cells. These antibodies had increased by more than 10 times in their blood and around seven times in their saliva, compared with samples taken just before vaccination. In contrast, the placebo group saw little change in antibody levels.
Importantly, the antibodies were still present six months later in the people who took the pill, albeit at lower levels, suggesting it could offer lasting immunity. “The fact that they’ve got this robust antibody response makes me hopeful that it could provide protection [against infection],” says Sarah Caddy at Cornell University in New York. “In particular, the saliva antibody response is a way we can get a snapshot of what’s happening in the intestine – because the immune responses there are similar,” she says.
But further work should explore whether the vaccine actually prevents infection or reduces the spread of norovirus, she says. The team hopes to explore this.
What’s more, the study focused on just one norovirus variant. “In the real world, there are dozens of different strains you might encounter – the vaccine may not protect against them all,” says Caddy. In unpublished work, the researchers found that a version of the vaccine containing both GI.1 and GII.4 norovirus variants – the latter of which is currently surging in the UK – generated antibodies against multiple variants, says Tucker.
This suggests we might soon have a norovirus vaccine, says Tucker. “If everything went smoothly, with no funding hiccups, a vaccine might be available in a couple of years,” he says.
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