Using data from all known human cases of two avian influenza A viruses, H5N1 and H7N9, researchers showed that an individual’s first exposure to infection by either virus provided lifelong protection against severe disease from novel strains within that same group, according to a recent study in Science.1
Researchers at the University of California, Los Angeles and the University of Arizona, Tucson reviewed 680 H7N9 cases from China (2013-2015), and 835 H5N1 cases from Cambodia, China, Egypt, Indonesia, Thailand, and Vietnam (1997-2015), and identified differences in susceptibility to each strain based on birth year. The dividing line for the two age groups was identified as the 1968 pandemic, “which marked the transition from an era of group 1 hemagglutinin circulation (1918-1968) to a group 2-dominated one (1968 to the present),” wrote the researchers. People born before 1968 are likely to have protection against H5N1, while those born during and after 1968 are more likely to have protection against H7N9.
The protective effects of being exposed to either strain in childhood were profound, providing “75% protection against severe infection and 80% protection against death for both H5N1 and H7N9,” observed the researchers.
The findings show that major patterns in zoonotic influenza A virus epidemiology are driven by birth year rather than patient age. “These findings challenge the current paradigm, where the entire population would be immunologically defenseless in a pandemic caused by a novel influenza virus,” said lead author Katelyn M. Gostic in a press release. “Our results suggest it should be possible to forecast age distributions of severe infection in future pandemics, and to predict the potential for novel influenza viruses from different genetic groups to cause major outbreaks in the human population.”2
- Gostic KM, Ambrose M, Worobey M, Lloyd-Smith JO. Potent protection against H5N1 and H7N9 influenza via childhood hemagglutinin imprinting. Science. 2016;354:722-726. doi: 10.1126/science.aag1322
- Childhood infections provide lifelong protection against flu viruses that come from animals [news release]. Los Angeles, CA: UCLA Newsroom; November 10, 2016.