Norovirus Vaccine Candidates Employ Different Approaches

Kerry Dooley Young

March 09, 2022

Scientists are trying different approaches to try to develop vaccines against norovirus, seeking to replicate the success seen in developing shots against rotavirus.

Speaking at the 12th World Congress of the World Society for Pediatric Infectious Diseases (WSPID), Miguel O’Ryan, MD, of the University of Chile, Santiago, presented an overview of candidate vaccines. Ryan has been involved for many years with research on rotavirus vaccines and has branched into work with the somewhat similar norovirus.

With advances in preventing rotavirus, norovirus has emerged in recent years as a leading cause of acute gastroenteritis (AGE) in most countries worldwide. It’s associated with almost 20% of all acute diarrheal cases globally, and with an estimated 685 million episodes and 212,000 deaths annually, O’Ryan and coauthors reported in a November 2021 review in the journal Viruses .

If successful, norovirus vaccines may be used someday to prevent outbreaks among military personnel, as this contagious virus has the potential to disrupt missions, O’Ryan and coauthors wrote. They also said people might consider getting norovirus vaccines ahead of trips to prevent traveler’s diarrhea. But most importantly, these kinds of vaccines could reduce diarrhea-associated hospitalizations and deaths of children. 

Takeda Pharmaceutical Company, for whom O’Ryan has done consulting, last year announced a collaboration with Frazier Healthcare Partners to launch HilleVax, Inc. Based in Boston, Massachusetts, the company is intended to commercialize Takeda’s norovirus vaccine candidate.

The Takeda-HilleVax candidate vaccine injection has advanced as far as phase 2 studies, including a test done over two winter seasons in US Navy recruits. Takeda and US Navy scientists reported in 2020 in the journal Vaccine that the primary efficacy outcome for this test could not be evaluated due to an unexpectedly low number of cases of norovirus. Still, data taken from this study indicate that the vaccine induces a broad immune response, the scientists reported.

In his WSPID presentation, O’Ryan also mentioned an oral norovirus vaccine candidate that the company Vaxart is developing, referring to this as a “very interesting approach.” 

Betting on the Gut

Based in South San Francisco, California, Vaxart is pursuing a theory that a vaccine designed to generate mucosal antibodies locally in the intestine, in addition to systemic antibodies in the blood, may better protect against norovirus infection than an injectable vaccine.

“A key ability to protect against norovirus needs to come from an intestinal immune response and injected vaccines don’t give those very well,” Sean Tucker, PhD, the founder and chief scientific officer of Vaxart, told Medscape Medical News in an interview. “We think that's one of the reasons why our oral approaches can have significant advantages.”

Challenges to developing a norovirus vaccine have included a lack of good animal models to use in research and a lack of an ability to grow the virus well in cell culture, Tucker said.

Vaxart experienced disruptions in its research during the early stages of the pandemic, but since has picked up the pace of its efforts to develop its oral vaccine, Tucker said during the interview.

In a recent filing with the Securities and Exchange Commission, Vaxart said in early 2021 it resumed its norovirus vaccine program by initiating three clinical studies. These included a phase 1b placebo-controlled dose ranging study in healthy elderly adults aged 55-80. Data from these trials may be unveiled in the coming months.

Vaxart said that this year it has already initiated a phase 2 norovirus challenge study, which will evaluate safety, immunogenicity, and clinical efficacy of a vaccine candidate against placebo.

Kerry Dooley Young is a freelance journalist based in Miami Beach, Florida. She is the core topic leader on patient safety issues for the Association of Health Care Journalists. Young earlier covered health policy and the federal budget for Congressional Quarterly/CQ Roll Call and the pharmaceutical industry and the Food and Drug Administration for Bloomberg. Follow her on Twitter at @kdooleyyoung

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