There’s been a recent surge in cases of the avian influenza A (H7N9) viral infection in China. As of this morning, there have been over a hundred reported cases and more than twenty deaths. The virus’ relatively sudden appearance in April, usually considered the end of flu season in the northern hemisphere, is eerily reminiscent of 2009’s H1N1 “swine flu” pandemic, which gained prominence at the same time of year, and which eventually infected sixty million people and killed more than twelve thousand. Is the world looking at a repeat pandemic?
Probably not. When examining a new influenza strain, scientists focus on two things. First, the virulence, or severity of the illness that the virus causes; and second, the communicability, or how easily the virus is passed from person to person.
As of today, dividing the number of confirmed cases by the number of deaths makes it look as though H7N9 is an especially bad flu, with a twenty-per-cent mortality rate. If true, this would be terrifying: the 1918 Spanish Flu, which has been called one of the deadliest plagues in human history, also had a mortality rate of around two per cent. But Tom Frieden, the director of the Center for Disease Control and Prevention, noted in an April 5th teleconference that that might not be the case with H7N9. “It could be that hundreds of other people have mild infections,” he said.