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The flu virus is always changing. Its genetic material, prone to mutations, is forever trying out new combinations to outwit a person's antibodies. Yet with all the changes going on, why are there so few strains circulating from year to year?
"Short-lived immunity," says University of California at Irvine researcher Robin M. Bush, Ph.D.
Dr. Bush and her colleagues Neil Ferguson, Ph.D., a mathematical biologist at Imperial College in London, and Alison Galvani, Ph.D., now at the University of California, Berkeley, have created a mathematical model that simulates how Type A and B flu viruses evolve. The group has found that, on its own, cross-immunity—the ability of antibodies against one flu strain to fight off another strain—would actually increase the number of mutant strains persevering. Only when a new type of immunity is factored in does the model more accurately reflect actual flu tracking data collected in the field.
According to Dr. Bush, for a few weeks or months after a person is exposed to one strain of the flu, he or she may be immune to reinfection by virtually any new strain that comes along. Such short-lived immunity would force most new mutations to die out immediately, keeping the total number of flu strains in check.
"If immunologists can identify the basis of such a response, we may be able to develop a vaccine that offers a less strain-specific, and thus longer-lasting, immunity to the virus," says Dr. Bush.
NM Ferguson et al. Ecological and immunological determinants of influenza evolution. Nature 422(6930):428-33. DOI: 10.1038/nature01509 (2003).
Last Updated March 12, 2013
Last Reviewed March 12, 2013