TOKYO -- As a new strain of stomach flu leaves a trail of stomach-clenching illness from Sydney to San Diego, scientists are moving closer to thwarting it for good.
Early stage human studies on a vaccine against norovirus, the top source of gastroenteritis in the United States, are set to finish this year. That would make work on the vaccine, developed by Takeda Pharmaceutical Co., the farthest along of several immunization candidates. A course of shots may confer lifelong protection against 95 percent of strains, said Rajeev Venkayya, who heads the Japanese drugmaker's vaccines unit.
A norovirus vaccine would be a boon to cruise ships, schools and nursing homes struggling to deal with a highly contagious, untreatable scourge. Of the 21 million people infected in the U.S. annually, about 800 die, mostly the very young and the elderly, according to the Centers for Disease Control and Prevention.
"Given the highly infectious nature of norovirus and its ability to cause extensive outbreaks in hospitals, elder-care facilities and cruise ships, there is a need for prophylactic and preventive approaches to guard against infection," said Peter White, a microbiology professor at the University of New South Wales in Sydney. A vaccine "would be particularly important for individuals with a high risk of exposure" or weakened immune defenses, he said.
White's lab last year helped characterize the new variant, dubbed GII. 4 Sydney for the city in which was first identified. The germ was responsible for the worst bout of gastroenteritis in a decade in Australia's Victoria state and has sparked outbreaks worldwide since March 2012.
Norovirus, also known as the winter vomiting bug, can be caught from an infected person, contaminated food or water, or by touching contaminated surfaces, according to the CDC. It causes the stomach and intestines to become inflamed, resulting in pain, nausea, diarrhea, and vomiting. Most outbreaks occur from November to April in the U.S.
If approved, Takeda's norovirus vaccine would be the first to protect people against the germ. It would potentially add as much as $400 million in annual revenue for the Osaka-based drugmaker, said Atsushi Seki, a health care analyst at Barclays in Tokyo.
In children younger than 5 years, norovirus caused 14,000 hospitalizations and 281,000 emergency room visits in 2009 and 2010 in the U.S., amounting to $273 million in annual treatment costs, the CDC said in a statement in March.
Takeda's vaccine candidate combines viral components from two norovirus types that laboratory studies suggest should fight all strains known to have circulated during the past 20 years, including the Sydney one, Venkayya said in an interview. Studies of the vaccine in healthy volunteers began in May 2012.
Takeda, Asia's largest drugmaker, plans further tests in children and the elderly, and a larger study to gauge the efficacy of one or two shots, he said, adding that it will be "several years" before the vaccine is ready for sale.
"I'm optimistic for this vaccine," he said. "It continues to look very good to us."
Takeda took over development of the vaccine when it bought Bozeman, Mont.-based LigoCyte Pharmaceuticals Inc. last year for an initial payment of $60 million. Takeda will pay LigoCyte more based on the vaccine's success. The acquisition is part of Takeda's strategy to tap the $25.3 billion global vaccines market.
Venkayya was previously director for global health delivery at the Bill & Melinda Gates Foundation, where he oversaw the foundation's work on polio eradication and introducing vaccines.
At least two other groups besides Takeda are developing vaccines against norovirus. UMN Pharma Inc., based in Yokohama, Japan, and Finland's University of Tampere are developing UMN-2003, which aims to protect against rotavirus, another cause of viral gastroenteritis. Charles Arntzen, professor of infectious diseases and vaccinology, is also working on one at Arizona State University in Tucson.
All three vaccine candidates are based on virus-like particles -- proteins that resemble key components of the virus, enabling the immune system to recognize and fight the pathogens.
Scientists are developing new weapons to fight norovirus years after they successfully produced vaccines against rotavirus. The delay reflects the difficulty of researching norovirus, which can't be grown outside the human body, said White at the University of New South Wales.
GlaxoSmithKline sold 360 million pounds ($556 million) of its Rotarix vaccine for rotavirus last year, while Merck & Co.'s RotaTeq generated $601 million.
While long-term care facilities and schools are especially prone to outbreaks, new epidemics of acute gastro often emerge on cruise ships, where control is hindered by close living quarters and shared dining areas. With regular turnover of passengers, noroviruses on ships can repeatedly infect new travelers, researchers at the Center for Infectious Disease Control in Bilthoven, Netherlands, found in a 2008 study.
This year, six cruise ships, including Celebrity Cruises Inc.'s Millennium, Solstice and Infinity, have had norovirus outbreaks on board, the CDC in Atlanta said.