Vaccine-In-A-Pill For Norovirus, The Infamous Winter Bug, Performs Well In Early Trials

When we say “vaccine” we immediately think “injection”, but there is a precedent for oral vaccines – most notably the oral polio vaccine that millennials of a certain age almost certainly received as a small children. 

In this case, the pill, called VXA-G1.1-NN, has been designed to deliver a harmless viral vector carrying a norovirus protein directly to the small intestine. This is not the only norovirus vaccine currently in trials – for example, a trial of an mRNA vaccine was launched in the UK last year – but developers Vaxart believe there are a lot of advantages to their pill format.

Writing on their website, they explain that the platform is adaptable to both existing and emerging diseases, avoids problems with storage, eliminates the risk of needlestick injuries, and promotes strong immune responses at mucosal barrier surfaces.

This last point is particularly important with norovirus. It means that, in response to the vaccine, the body builds its defenses right at the places where the virus is likely to try and gain entry – the lining of the nose and mouth, for instance. 

“Given that norovirus is transmitted through mucosal routes, a vaccine that elicits protective immunity at barrier surfaces would be desirable,” write the study authors in their paper. 

Norovirus outbreaks are so hard to control because as few as 10 viral particles are enough to spark an infection. The virus is not easily killed by hand sanitizers, so regular soap and water and surface cleaners with bleach are the best tools we have to stop it. However, given that someone who’s been struck down with the disease can remain infectious for weeks after their symptoms have gone, it’s easy to see how the virus can spread like wildfire in settings like schools, care homes, and cruise ships. 

Most people will recover from a bout of norovirus within a few very unpleasant days, but the consequences can be much more serious in older people. Severe vomiting and diarrhea bring a risk of dehydration, which can be deadly if not treated. 

Unfortunately, it’s precisely this group of people who are more difficult to target with vaccines. The immune system starts to wind down a bit as we age, thanks to a process called immunosenescence. Basically, it becomes harder to elicit a strong response from it with a vaccine.

Add to that the fact that norovirus is not just one virus, but rather a group of them, and you have a complex problem on your hands.

However, Vaxart’s candidate vaccine pill appears to be hitting the right notes. In the trial, 65 adults aged 55-80 were stratified into three cohorts – low, medium, and high dose – and a placebo group. They were further divided into younger (55-65) and older (66-80) age groups. 

Each treatment group was given two pills, with the second 28 days after the first as a booster. The vaccine was found to be safe, with no serious adverse events occurring.

Better still, it was effective. The team found that the pills elicited a strong antibody response in blood, saliva, and nasal secretions. The mucosal immunity lasted for 210 days, showing it was not a short-term response. 

“The mucosal response induced by VXA-G1.1-NN has the potential to inhibit infection, viral shedding, and transmission,” the authors conclude. While additional, larger trials will now be needed, they believe it is a positive first step. So much so, Vaxart just announced they are launching a Phase 1 trial for a second-generation norovirus vaccine pill, to run concurrently. 

For anyone who was struck down during the worse-than-usual norovirus season that hit UK and US headlines recently, this will be music to their ears.

The study is published in the journal Science Translational Medicine.