An oral vaccine could combat norovirus

MADRID (EFE).— Norovirus is one of the leading causes of gastrointestinal infections worldwide. Now, an oral vaccine has been able to generate strong immune responses in the mucosa and even reduce the spread of the virus in inoculated volunteers.

These are the results of a Phase 2 clinical trial sponsored by Vaxart, Cincinnati Children's Hospital Medical Center, and Stanford University, Maryland University in Baltimore, and Harvard University. Details are published in the journal Science Translational Medicine.

“The promising evidence of the vaccine's efficacy supports its potential to address the lack of safe and reliable vaccines against norovirus, a leading cause of gastrointestinal infections worldwide,” the publication describes.

Norovirus typically causes vomiting, diarrhea, and stomach cramps, and in some patients, symptoms can be so severe that they require hospitalization and intravenous fluid therapy. It is also extremely contagious and easily transmitted through water and food, making it very common in schools, hospitals, cruise ships, and other high-density areas.

There are no licensed vaccines that can prevent infections, the study notes. To bridge this gap, the team led by Becca Flitter of the US biotechnology company Vaxart evaluated the potential of VXA-G1.1-NN, an oral tablet vaccine they had previously developed and tested in rodents and in a Phase 1 trial.

In the largest Phase 2 trial, scientists administered either the vaccine or a placebo to 165 volunteers. They found the tablet was safe, well-tolerated, and produced significant antibody responses against the virus's VP1 protein, including in nasal fluid, saliva, and stool samples.

They exposed participants to norovirus GI.1 and found that the vaccine provided protection against infection.

Those volunteers who received the vaccine shed less virus in their feces, suggesting that it could combat a potent factor in the transmission of the pathogen, the journal notes.

The vaccine candidate is formulated as a heat-stable tablet, reducing the need for specialized infrastructure or qualified professionals to administer it, facilitating its rapid distribution.

“These results demonstrate the potential of VXA-G1.1-NN as a safe and effective oral norovirus vaccine and reveal crucial immunological features that underpin its efficacy,” the authors write in their article.

However, they also admit limitations, such as the fact that the GI.1 genotype of norovirus was specifically investigated, when GII.4 has been more prevalent over the past 20 years.

For María Dolores Fernández García, head of the National Reference Laboratory for Gastroenteritis-Producing Viruses at the National Center for Microbiology, the work represents a significant advance in the development of biological agents against norovirus.

“Although the study's efficacy results may be considered 'modest' (a 30% relative reduction in qPCR-detectable infection and a 21% reduction in norovirus gastroenteritis), they remain clinically relevant in the context of vaccine development against norovirus, a virus that has historically presented significant challenges in obtaining effective vaccine protection.”

Although these levels of protection are below the ideal threshold expected for a vaccine, they are consistent with what has been observed in other Phase 2 norovirus dose studies.

One notable aspect is that, being oral, it not only facilitates the induction of an immune response in the mucosa (something more difficult to achieve with injections), but also makes its distribution and application easier, especially in settings with limited resources, adds the researcher, who did not participate in the trial.

However, it will be crucial to test it in these settings and with key populations, such as children and older adults, who are more vulnerable to norovirus infections.

The trial was conducted exclusively on healthy adults aged 18 to 49.