CDC: H1N1 declining but still widespread

Nov 20, 2009 (CIDRAP News) – Pandemic H1N1 influenza activity is showing further signs of declining around the country but remains very widespread, the Centers for Disease Control and Prevention (CDC) reported today.

The virus was widespread in 43 states last week, compared with 46 a week earlier, the CDC said in its H1N1 Situation Update. Visits to doctors for flu-like illness dropped for the third week in a row, and flu-related hospitalization rates began to decline as well. But both variables remained above normal for this time of year.

Another 21 flu-related deaths in children were reported last week, including 15 involving confirmed H1N1 infections, the CDC said. That raised the total of confirmed H1N1 pediatric deaths to 171.

"We are beginning to see some declines in influenza activity around the country, but there's still a lot of influenza everywhere," said Dr. Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases, at a news briefing today.

Flu activity is "still much greater than we would ever [normally] see at this time of year," she said.

All 10 federal regions are starting to see declines in flu activity, but activity is still increasing in some states, including Maine and Hawaii, Schuchat reported.

She stressed that the pandemic remains unpredictable and that she didn't know if it has peaked: "We don't know if these declines will persist, what the slope will be, whether we'll have a long decline or it will start to go up again."

On the vaccine supply front, Schuchat said a total of 54.1 million doses have been made available, an increase of 11 million over a week ago. As of 2 days ago, 93% of the available doses had been ordered by the states, she added.

Meanwhile, manufacturers reported that 94.5 million doses of seasonal flu vaccine had been distributed as of Nov 13, she said. The CDC has predicted that the seasonal vaccine supply will total about 115 million doses.

Regarding the deaths in children, Schuchat said about two thirds of the children had an underlying condition such as asthma, cerebral palsy, or muscular dystrophy. A common factor in those who were previously healthy has been bacterial co-infections, which point to the importance of pneumococcal vaccines, she noted.

H1N1 mutation in Norway
Schuchat also commented on reports that surfaced today of a mutation in H1N1 viruses found in three patients in Norway. The World Health Organization (WHO) said today that the mutation was found in the first two fatal H1N1 cases in Norway and in one patient with severe illness.

"What I can say is the mutation that was identified has no implications for how good the match of the vaccine is and it has no implications for treatment with antiviral medicines, but it's important to track and look for changes," Schuchat said.

She further said the mutation has been seen sporadically around the world in both severe and mild cases. "There's some theoretical reasons why this particular mutation might lead an influenza virus to live easier in the deep part of the lungs and cause lower respiratory infections, but we've actually seen lower respiratory infections in severe viral pneumonia without this mutation," she said. "So I think it's too soon to say what this will mean long term."

The WHO said the mutation does not appear to spread and the public health significance of the finding is unclear.

"Although further investigation is under way, no evidence currently suggests that these mutations are leading to an unusual increase in the number of H1N1 infections or a greater number of severe or fatal cases," the agency said.

The statement said the mutated virus remains sensitive to oseltamivir and zanamivir, and studies show that existing pandemic vaccines provide protection.

See also:

Nov 20 CDC Situation Update

Nov 20 WHO statement

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