Focus on the Flu

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.

This information is based on the following article:

• "Ecological and Immunological Determinants of Influenza Evolution," in Nature
  

  
  

• Dr. Bush's laboratory Web page on the University of California, Irvine Web site