Flu protein changes can alter outbreak

Tom Corwin

Oct. 30, 2009 (McClatchy-Tribune Regional News delivered by Newstex) -- Changes in a key protein of the influenza virus can help predict the severity of outbreak, and even how long people remain infectious, according to a University of Georgia researcher.

The amount of pre-existing immunity across the population also plays a role and could help explain the unusual impact of the novel influenza A H1N1 virus in younger people.

In a paper published today in the journal Science, an international team led by Andrew W. Park looked at a model for flu transmission and the virus' ability to mutate in order to escape the host's immune system.

Change as small as a two amino acid difference between the circulating virus and the virus from a past immunization or infection can raise the risk of infection.

That in turn influences how many in the overall population are infected, with greater difference producing greater outbreaks, said Dr. Park, an assistant professor in the Odum School of Ecology and in the College of Veterinary Medicine.

The ability to produce those changes becomes an adaptation that helps the virus escape the immune system of those with some level of pre-existing protection.

"Like many of these RNA viruses it is routinely making errors as it replicates so it is spinning off these mutants all the time and that's clearly part of its life history," Dr. Park said.

The study was done with equine influenza virus so he cautioned about trying to apply the findings broadly.

But the study also conversely showed that a mismatch between virus strains could be somewhat minimized by increasing the number vaccinated.

"We know that influenza can change fairly rapidly and we know that sometimes vaccines take a little while to manufacture and dispatch," Dr. Park said.

"It's trading off between the quality, in terms of the genetic closeness, and the quantity that's required in terms of the number of people vaccinated, which was a quite interesting result," he said.

The findings fit in well with earlier work by Jackie Katz, of the Centers for Disease Control and Prevention, on the 2009 H1N1 virus that found cross-reactive proteins in many people born before 1950 and little in those born after 1980, suggesting that older people had some protection from being exposed to a similar flu strain.

It could help explain why younger people seem hardest hit by the new virus but it causes relatively little illness in the elderly, who are normally among the most vulnerable to flu.

Moving from thinking about individual immunity to the immunity of people as a whole is how some are now reordering their thinking about flu, Dr. Park said.

"Starting to think about immunity at the population level is a really important step forward," he said.

Reach Tom Corwin at (706) 823-3213 or tom.corwin@augustachronicle.com.

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