Will the H1N1 flu virus mutate?

Originally published in MedPage Today

by Michael Smith, MedPage Today North American Correspondent

The CDC is keeping a careful eye on a mutation in some strains of the pandemic H1N1 flu that Norwegian researchers isolated from three patients with severe disease.

The mutation has been seen “sporadically” in the U.S., according to Anne Schuchat, MD, director of the CDC’s National Center for Immunization and Respiratory Diseases.

But in the U.S., the mutation has been associated with mild disease, she said, although the Norwegians isolated it from the first two patients who died of the disease in that country.

The mutation was also found in a third patient who had severe disease, according to a statement from the Norwegian Institute of Public Health.

Schuchat told reporters that there are “theoretical reasons” for thinking that the mutation might make it easier for the virus to penetrate to the lower lungs, leading to more severe disease.

But she said in the U.S., patients have had severe lower respiratory infections caused by strains without the mutation, as well as mild disease caused by strains with the mutation.

“It’s just too soon for us to say what this is going to mean long term,” Schuchat said. “It’s an important finding for the influenza virologists, and they’re looking into it.”

She added that the mutation “has no implications for how good the match of the vaccine is and no implications for treatment with antiviral medicine.”

“But it’s important for us to continue to track influenza viruses and look for changes,” she said.

The agency will be watching to see if the mutation spreads and if it is more common in cases of severe disease, she added.

Schuchat said influenza-like activity in the U.S. continues to be high, although the number of states reporting widespread disease has dropped slightly — to 43 states from 46 last week.

At the same time, she said, some states — such as Maine and Hawaii — are reporting increased activity this week.

Overall, flu activity is “much greater than we would ever see at this time of the year,” Schuchat said.

The CDC has had reports this week of an additional 21 pediatric deaths associated with the flu, 15 of them confirmed to be H1N1. The other six could not be subtyped but were influenza A and probably H1N1, Schuchat said.

Two-thirds of the 171 lab-confirmed H1N1 pediatric deaths have involved children with underlying conditions, such as asthma or cerebral palsy, she said.

The vaccine supply is still less than the agency had hoped for, she said, but a total of 54.1 million doses have become available since the beginning of the season.

Of those, Schuchat said, states have ordered 93%.

She added that vaccine manufacturers have told the CDC that 94.5 million doses of the seasonal flu vaccine have been distributed.

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