Opinion

Commentary: Norovirus vaccine candidates employ different approaches


 

Norovirus, as noted above, is now the most common cause of medically attended acute gastroenteritis (AGE) in the United States. Norovirus AGE resembles rotavirus AGE, but a bit heavier on the vomiting. What makes it scary is that it is a low-inoculum infection (as few as 16 virus particles can cause infection), and it survives for prolonged periods in food, 10% chlorinated water, and on environmental surfaces (J Med Virol 2008;80:1468-76); hence, the infamous outbreaks on cruise ships and daycare centers. So a vaccine would be very welcome. The two non-Chinese candidates GI.1/GII.4 vaccines are Takeda’s VLP vaccine and Vaxart’s oral adenovirus vector-based vaccine.
Takeda’s is injectable. If VLP sounds familiar, VLPs make up the FDA-approved HPV vaccine we use. Two doses of various formulations were tested in a recent phase 2 study of 1- to 3- and 4- to 8-year-olds in Finland, Panama, and Colombia with no safety issues identified. The 1- to 3-year-olds responded somewhat better than 4- to 8-year-olds, and titers remained elevated up to day 210 (Vaccine. 2022 Jun 9;40[26]:3588-96).

A recently as yet unpublished phase 1b trial of Vaxart’s vaccine in 55- to 80-year-olds (NCT04854746) showed a dose-dependent response. IgA mucosal cell responses were similar to those in younger adults. Adverse event profiles were similar between vaccinees and placebo recipients.

Progress continues for both vaccines, but we await efficacy trials. We are likely still years from a pediatric vaccine. My sense is that an oral vaccine would be more readily accepted into the pediatric schedule, but how to incorporate it and not cause issues with the rotavirus vaccine will need evaluation.

Christopher J. Harrison, MD, is professor, University of Missouri Kansas City School of Medicine, department of medicine, infectious diseases section, Kansas City. He has no financial conflicts of interest.

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