May 17, 2013
The incidence of H7N9 transmission to humans has lessened, but it is unknown whether fewer cases signal a subsiding problem, or something else.
From May 2-16, Chinese authorities reported just seven new cases of the novel H7N9 human infection. Just 24 cases were reported from April 24, through May 16. Unfortunately, the fatality rate among H7N9 victims remains alarmingly high.
Eleven fatalities were reported during the three-week span ending May 16, including nine from May 1-15. A total of 34 fatalities have been reported.
A total of 134 H7N9 cases have been confirmed and the fatality rate is approximately 25 percent. Although a huge disparity in the numbers makes comparison difficult, the massive flu pandemic of 1918 featured a fatality rate of just above 1 percent.
Easily the largest flu pandemic of the 20th century, the 1918 flu pandemic claimed more than 600,000 American lives. The death toll worldwide was thought to be nearly 60 million.
Government health authorities on three continents continue to share information and allocate resources in an effort to learn more about the H7N9 virus. There remains no evidence of sustained human-to-human virus transmission, and no cases have been confirmed outside of Mainland China.
Meanwhile, the Chinese have moved to enhance disease control by temporarily closing some poultry markets linked to the H7N9 outbreak to date. More than 75 percent of currently known H7N9 human cases involve contact with chickens, ducks or other live poultry.
Some avian flu experts theorize that the recent lessening of H7N9 activity may be linked to seasonal climate changes. Influenza is often most active during colder months.
On April 11, CDC received the first H7N9 virus isolate from China. The isolate is being used to develop an H7N9 vaccine. If a vaccine is actually needed, it should be available during the cold-weather months.
More information about the H7N9 virus will be available on this site. Please check back with us periodically for updates.