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A thorough investigation into the immune responses of participants revealed not only a systemic response but also reactions within distant mucosal areas. Blood analyses showed a notable increase in two antibody types, IgA and IgG, post-vaccination when compared to those receiving a placebo. The high-dose group exhibited the most significant immunological response.
Tests designed to estimate neutralizing antibodies against norovirus indicated that the vaccine’s antibodies could potentially hinder viral activity. Further examinations confirmed that cellular immune responses were activated, suggesting that the systemic responses could provide protection in areas beyond the intestines, specifically in the mouth and nasal passages. Salivary tests and nasal swabs detected substantial increases in secreted IgA against norovirus.
Immune responses were most pronounced within the first two months following vaccination, tapering off over time, yet some effects were observed to last for nearly seven months. When researchers examined the two age groups, 55–65 and 65–80, they found no notable disparities in immune reactions, indicating the vaccine’s efficacy was consistent across older individuals.
The team at Vaxart concluded that the vaccine demonstrated the possibility of inhibiting infection, viral shedding, and transmission. They noted that “the administration of VXA-G1.1-NN in older adults led to robust and durable immunogenicity detected both in circulation and across multiple mucosal sites,” highlighting a promising result considering the typical decline in cellular and mucosal immunity among older populations.
Challenges Ahead
However, the findings are not without caveats. Despite the statistically meaningful increase in immune responses during this small initial trial, the correlation to real-world protection remains uncertain. In 2023, Vaxart published data from a challenge study involving 141 participants, including 76 who received the vaccine and 65 who received a placebo, exposing them deliberately to norovirus to assess the vaccine’s protective capabilities. The outcomes were less than encouraging: 53 individuals in the placebo group (approximately 81.5 percent) became infected with norovirus, as confirmed by PCR testing of their stool samples, while 76 vaccinated participants (60 percent) also contracted the virus. This resulted in the vaccine providing only a 29 percent reduction in relative risk of infection.
When evaluating symptomatic infections, the vaccine showed a protective efficacy of around 21 percent; 34 vaccinated individuals (48 percent) and 37 in the placebo group (57 percent) experienced symptoms of acute gastroenteritis.
Source
arstechnica.com