Norovirus Vaccine Works on Common Strain

Laird Harrison

October 06, 2013

SAN FRANCISCO — An investigational vaccine being developed by Takeda Pharmaceutical Company is effective against the most common strains of norovirus, a new study shows.

Vaccinated people were half as likely to suffer severe symptoms compared with those not vaccinated who swallowed water laced with strains of the virus, said lead investigator David Bernstein, MD, from the University of Cincinnati, in Ohio.

"In a nutshell, we found there was protection from vomiting and diarrhea, the most common symptoms of norovirus infections," he told reporters attending a news conference here at IDWeek 2013.

A power outage at the Moscone Center, where the study was scheduled to be presented, forced Dr. Bernstein to delay his formal talk from the morning to the afternoon on Saturday, October 5.

Another vaccine has already reduced the prevalence of rotavirus, making norovirus the most common cause of gastroenteritis and a prime target of immunologists, Dr. Bernstein said at the meeting. Nearly everyone has suffered an infection from the virus, he added.

The disease sickens an estimated 21 million people in the United States every year and kills 800.

Making a norovirus vaccine has proved challenging because the virus cannot be cultivated and there are no animal models for the disease, Dr. Bernstein explained.

The researchers took a new approach, expressing norovirus capsid protein to create viruslike particles that cannot cause the disease but nevertheless stimulate an immune response.

A previous study showed that the vaccine worked against the Norwalk strains of the virus, also known as GI.1. Dr. Bernstein estimated that GII.4 strains cause about 60% of norovirus infections and that GI.1 strains cause an additional 10% to 20%.

For the new study, Dr. Bernstein and his team randomly divided 98 healthy adults into 2 groups. They injected the vaccine in 2 doses, 28 days apart, to half the patients and gave the rest a placebo.

Both groups drank water containing the GII.4 strain of the virus, the most common strain.

Thirty days later, those vaccinated were less likely to develop an infection and were less likely to have severe symptoms if they fell ill. The researchers categorized patients on the basis of what the patients reported about their condition.

Those who said they suffered severe symptoms were bedridden and were feeling awful, said Dr. Bernstein.

Table. Patients with Norovirus Suffering Vomiting or Diarrhea

Outcome Vaccinated (%) Unvaccinated (%) P -Value
Developed infection 52 60

Mild, moderate, or severe symptoms

18 38 .042

Moderate or severe symptoms

20 42 .068

Severe symptoms

0 8 .054

Dr. Bernstein cautioned that the results of this trial, in which a carefully controlled intentional infection was used, cannot be extrapolated to the general population subjected to wild strains of the virus. That research will come next.

He also said it is not clear how long immunity from the vaccine might last. "We certainly hope that it's longer than 1 season," Dr. Bernstein told Medscape Medical News. Although norovirus strains are evolving, they do not change as fast as influenza strains, he pointed out.

But even a 1-season vaccine would be useful, Dr. Bernstein said. For example, passengers might be vaccinated just before an ocean cruise. Soldiers might be vaccinated when they are in close quarters. And nursing home residents might benefit ― even if they needed revaccination each year.

Andrew Pavia, MD, from the University of Utah in Salt Lake City, said he agrees with Dr. Bernstein's assessment.

The short-term benefits are very, very attractive even if it doesn't lead to long-term immunity or eradicate the disease. Dr. Andrew Pavia

"The short-term benefits are very, very attractive even if it doesn't lead to long-term immunity or eradicate the disease," he said.

The researchers found no severe adverse reactions associated with the vaccine, though some patients reported soreness at the injection site, Dr. Bernstein said.

Plans are under way for the vaccine to proceed to phase 3 trials, and it is expected to take at least 5 years to reach the market.

This study was funded by Takeda Pharmaceutical Company. Dr. Bernstein is a consultant for the company. Dr. Pavia has disclosed no relevant financial relationships.

IDWeek 2013. Abstract LB-2. Presented October 5, 2013.


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