Norovirus cases are currently higher than they have been in over a decade, according to the CDC.
Currently, there’s no antiviral treatment or vaccine for norovirus. However, Moderna scientists are in the late stages of testing a potential mRNA vaccine. This article details norovirus and the progress of vaccine development.
The Current Norovirus Surge
Dr. Edmund Milder, a pediatric infectious disease specialist, explains that norovirus, commonly known as the stomach flu, is a leading cause of gastroenteritis, characterized by vomiting and diarrhea.
With nearly 50 subtypes, different norovirus strains circulate yearly. For a decade, GII.4 was dominant, but GII.17 is now prevalent. This shift may account for the increased cases, as immunity to previous strains doesn’t guarantee protection against this new one.
Norovirus Symptoms
Typical symptoms include vomiting, diarrhea, and dehydration. While usually mild and self-limiting, older adults and infants can experience more severe illness. Annually, approximately 100,000 hospitalizations and nearly 1,000 deaths, primarily among the elderly and young, occur in the U.S., mainly due to dehydration.
Norovirus: Unique Characteristics
Norovirus differs significantly from other viruses. Infectivity is exceptionally high; as few as 10 virus particles can cause illness.
The virus’s hardy outer shell enables survival for days on surfaces. Hand sanitizer is ineffective; thorough handwashing with soap and water for 20 seconds is crucial. High heat or cold temperatures don’t eliminate it. A diluted bleach solution applied for at least five minutes is the most effective surface disinfectant.
Challenges in Norovirus Vaccine Development
Dr. Doran Fink, therapeutic head of gastrointestinal pathogens and bacterial vaccines at Moderna, explains that the virus’s many genotypes require different immune responses for protection. Any vaccine must predict circulating strains, much like the annual flu vaccine.
Progress on the Norovirus Vaccine
Moderna is conducting a phase 3 trial with 25,000 participants worldwide, following encouraging early results. The mRNA vaccine generated antibodies effectively blocking the norovirus protein in lab tests; placebo recipients did not show this antibody activity.
To address the numerous strains, Moderna’s candidate includes three norovirus types. This multivalent approach aims for broad protection, mirroring their strategy for the mRNA flu vaccine. The mRNA platform allows for quicker adaptation to evolving strains.
The bivalent approach, similar to a COVID-19 vaccine, has proven effective against multiple viral strains.
Moderna anticipates completing enrollment this spring and will follow participants for at least six months. Determining real-world effectiveness requires a sufficient number of infections for comparison. International trial sites enhance data collection.
Vaccine Effectiveness
Similar to the COVID-19 vaccine, this norovirus candidate aims to reduce severe illness and hospitalization, not necessarily prevent infection.
Protecting Yourself from Norovirus
In the absence of antiviral treatments or vaccines, good hygiene is crucial. Frequent handwashing and avoiding touching the face and mouth are vital. If ill, stay home to prevent spreading the virus, which can be shed for days or weeks after symptom resolution.