The death rate from the pandemic H1N1 swine flu is likely lower than earlier estimates, an expert in infectious diseases said on Wednesday.

New estimates suggest that the death rate compares to a moderate year of seasonal influenza, said Dr Marc Lipsitch of Harvard University.

“It’s mildest in kids. That’s one of the really good pieces of news in this pandemic,” Lipsitch told a meeting of flu experts being held by the U.S. Institute of Medicine.

“Barring any changes in the virus, I think we can say we are in a category 1 pandemic. This has not become clear until fairly recently.”

The Pandemic Severity Index set by the U.S. government has five categories of pandemic, with a category 1 being comparable to a seasonal flu epidemic.

Seasonal flu has a death rate of less than 0.1 percent - but still manages to kill 250,000 to 500,000 people globally every year.

A category 5 pandemic would compare to the 1918 flu pandemic, which had an estimated death rate of 2 percent or more, and would kill tens of million of people.

An estimate published in the journal Eurosurveillance last month by the French Institute for Public Health Surveillance put the mortality rate far higher, at 0.4 percent for all age groups.

HIGHER MORTALITY?

Lipsitch took information from around the world on how many people had reported they had influenza-like illness, which may or may not actually be influenza; government reports of actual hospitalizations and confirmed deaths.

He came up with a range of mortality from swine flu ranging from 0.007 percent to 0.045 percent.

Either way, having new information about how many people were infected and did not become severely ill or die makes the pandemic look very mild, he said.

“The news is certainly better than it was in May and even better than it was at the beginning of August,” Lipsitch said.

But another expert cautioned this does not mean the pandemic will not have severe effects on people and communities because it will infect more people than seasonal flu usually does in any given year.

“This is not a severe pandemic,” said Dr. Jeffrey Duchin of Seattle & King County Public Health and the University of Washington.

“We are going to see probably twice as many people die from the flu as we do in a typical flu season. That is tens of thousands of people. And many of these people are going to be younger.”

H1N1 swine flu was declared a pandemic in June after flashing around the world in six weeks, in part because most people have virtually no immunity to it. Experts all said a true death rate would not be clear for weeks because it is impossible to test every patient and because people with mild cases may never be diagnosed.

This lack of information made the epidemics in various countries and cities look worse at first than they actually were, Lipsitch said. People sick enough to be hospitalized are almost always tested first.

“Yes, there’s been hype, but I don’t think it’s been an outrageous amount of hype,” Lipsitch said.

Seasonal flu is usually far worse among the elderly, who make up 90 percent of the deaths every year. In contrast, this flu is attacking younger adults and older children, but they are not dying of it at the same rate as the elderly do during seasonal influenza, Lipsitch said.

(Editing by Eric Beech and Eric Walsh)
By Maggie Fox, Health and Science Editor