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Avian flu virus re-emergence would present potential risk to under-50s
Often public health guidelines stress the vulnerability of older people to influenza infections and vaccine programmes are targeted towards elderly people and other vulnerable groups. However, a new study suggests that people under the age of 50 may be more vulnerable to infection if avian flu re-emerged in humans.

The study by researchers from St. Jude Children's Research Hospital in Memphis, Tennessee suggests that avian H2N2 viruses circulating in birds remain antigenically similar to the pandemic A/Singapore/57 (H2/N2) virus which caused a devastating pandemic, estimated to have killed 1-2 million people, when it emerged in humans in 1957-1958. This research group, who are a National Institute of Allergy and Infectious Diseases Centre of Excellence for Influenza Research and Surveillance, published their findings in the prestigious Journal of Virology, in an advance online edition. The study suggests that people under the age of 50 could be particularly vulnerable if the avian virus re-emerged in humans via ‘gene-swapping’ as younger people would have no previous exposure and therefore no humoral immunity to the virus.

The study findings were based on risk assessment of a panel of 22 avian H2N2 viruses isolated from both wild and domesticated birds over sixty years. The researchers found that the rate of antigenic and genetic evolution was very low, meaning that the viruses remain antigenically similar to the isolates in circulation at the time of the pandemic. Most of the isolates were able to replicate both in mice and human bronchial epithelial cells. Worryingly, many of them also replicated in ferrets, considered to be a reliable model for influenza replication in humans. The virus could be transmitted via direct contact between cage-mates but were not airborne. More reassuringly, the group did not observe markers of mammalian adaptation in the important proteins, haemagluttinin (HA) and the PB2 subunit of the viral RNA polymerase, in any isolates, and they retained a preference for avian-like α2-3 linked sialic acid receptors. Also, all were susceptible to anti-viral medications including neuraminidase inhibitors and adamantanes and their similarity to pandemic A/Singapore/1/57 (H2N2) virus suggests they would be controllable by the pandemic vaccine candidate.

Nevertheless, the group urges caution as the avian H2N2 viruses showed such a sustained pathogenicity in multiple mammalian models. Thus they still present a risk for human infection. The answer is for the public health and biotechnology community to be vigilant and maintain continual surveillance as part of pre-pandemic planning.


St. Jude Children's Research Hospital. "1950s pandemic influenza virus remains a health threat, particularly to those under 50." ScienceDaily, 3 Dec. 2013. [Accessed 4 Dec. 2013].

Jones, J.C., Baranovich, T., Marathe, B. M., Danner, A. F., Seiler, J. P., Franks, J., Govorkova, E. A., Krauss, S. and Webster, R. G., 2013. Risk Assessment of H2N2 Influenza Viruses from the Avian Reservoir. Journal of Virology, 2013; DOI: 10.1128/JVI.02526-13
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