Study confirms low mortality for H1N1 flu, but CDC director says threat isn't over

WASHINGTON — One of the most systematic looks yet at the H1N1 flu pandemic confirms that it is at worst only a little more serious than an average flu season and could well be a good deal milder, researchers said.

They analyzed data from Milwaukee and New York, two U.S. cities that have kept detailed tabs on outbreaks of H1N1, to calculate a likely mortality rate of 0.048 percent, according to Reuters’ report Dec. 7.

"That is, about 1 in 2,000 people who had symptoms of pandemic H1N1 infection died," Dr. Marc Lipsitch of Harvard University’s School of Public Health and his colleagues wrote in PLoS Medicine, a Public Library of Science journal.

"It is probably going to be the mildest pandemic on record — compared to the three that happened in the 20th century," Lipsitch told National Public Radio.

Probably 1.44 percent of patients with H1N1 who were sick enough to have symptoms were hospitalized, and 0.24 percent required intensive care, the analysis’ authors wrote.

The findings should be reassuring to public health officials and policymakers who worry that a flu pandemic could kill millions and worsen the global recession.

They do not, however, guarantee that H1N1 will not worsen, or that some other, stronger, strain of flu will not emerge.

Health experts agree it is impossible to count precisely how many people have been sickened by H1N1, which was declared a pandemic in June.

Few people are tested, tests are inaccurate and many people only have mild illness. So careful projections give a more accurate picture of a pandemic than actual counts of confirmed illnesses and deaths.

Lipsitch specializes in these sorts of calculations and a global estimate he did in September gave similar projections.

One open question is how many people have actually been infected. The U.S. Centers for Disease Control and Prevention estimated in November that number was 22 million Americans.

Lipsitch's team calculated a potential range of 7,800 to 29,000 deaths.

This compares to seasonal flu, which kills 36,000 people a year and puts 200,000 into the hospital.

Last spring, experts thought it was entirely possible swine flu would kill 1 out of every 100 people who got the virus.

"We now know that's at least 20-fold too high and probably more than 20-fold too high," Lipsitch said.

The big difference this year is that most of those deaths have been among children, teenagers and adults under age 50. Flu typically kills mostly people over 65.

But that's not because this flu is more severe among children and young adults, as many think. It's simply because many more young people are getting the flu than usual.

"And what you find is that the pandemic is making more kids sick. But it's killing a smaller percentage of the kids it makes sick than it is of the adults and seniors it makes sick," said Peter Sandman, an expert in risk communication.

He told NPR that the CDC has been reluctant to acknowledge that H1N1 flu has been much milder than expected.

"The CDC may be thinking, you know, 'There are already millions of people who plan not to get vaccinated because they think the pandemic is mild, and if we announce as the official health agency of the U.S. government that the pandemic is mild, than even fewer people will get vaccinated and some of those people will die,'" he said.

Not so, says the CDC’s director, Dr. Thomas Frieden.

"I think we've been completely transparent with what we think is happening. I think we have a difference of opinion on whether that is mild or severe," he told NPR.

He points out that the CDC has counted more than 250 deaths among children.

"Any flu season that kills at least three times more children than a usual flu season — I think it would be very misleading to describe that as mild," he said.

But Frieden agrees that perception matters. The more that people think the pandemic threat is over, the fewer who will get vaccinated.

Experts worry that could increase the chance of a third wave of swine flu early next year.