Dec. 4 (Bloomberg) — The World Health Organization, facing criticism that it exaggerated the threat of swine flu, said it’s too soon to decide whether the pandemic is more or less deadly than seasonal flu and comparing death rates may be misleading.

Mortality from the new H1N1 strain is “unquestionably higher” than the death toll reported by national authorities, the Geneva-based agency said in a report seen by Bloomberg News before its scheduled publication today. Deaths totaled more than 7,820 as of Nov. 22, said WHO, which estimates as many as 500,000 people die each year from seasonal strains.

Health authorities worldwide are assessing whether their response to swine flu is justified by its threat as cases of flu-like illness retreat in the U.S. and U.K. While a majority of patients recover within days and reported fatalities are a fraction of the seasonal flu toll, these figures mask the full impact of swine flu on society, WHO said.

“Compared with seasonal influenza, the H1N1 virus affects a much younger age group in all categories — those most frequently infected, hospitalized, requiring intensive care, and dying,” WHO said in the report.

In Australia, about 3,000 people aged 50 or older die from seasonal flu each year, according to statistical modeling. Officials counted 190 deaths associated with confirmed swine flu, Jim Bishop, the nation’s chief medical officer, said last week in a report in the New England Journal of Medicine.

Younger Victims

The median age of patients who died was 53, compared with 83 in seasonal epidemics, and the number of patients treated in intensive care units for viral pneumonia was about 14 times greater than normal, Bishop said in a telephone interview from Canberra today.

“It’s a different type of virus affecting younger people and putting more people into hospital and ICU,” he said. “It’s not attacking older people in nursing homes.”

The pandemic’s impact is better gauged by the number of life-years lost because of the younger age of victims compared with seasonal flu, said Michael Osterholm, director of the University of Minnesota’s Center for Infectious Disease Research and Policy in Minneapolis.

“If you look at years of personal life lost, it’s much higher, and that’s the point we have to get across,” Osterholm said in a telephone interview today. “A death in an otherwise healthy 24-year-old, to me, is a major defeat for society.”

Pregnant Women

Of those infected worldwide, 1 percent to 10 percent have required hospitalization and as many as a quarter of those patients have needed intensive care, WHO said today in the Weekly Epidemiological Record newsletter. Pregnant women have a 10 times higher likelihood of requiring admission to an ICU compared with the general population, and at least 1 in 14 of all hospitalized cases are women in their second or third trimester of pregnancy, it said.

Bishop said WHO’s decision to declare swine flu a pandemic in June helped guide the nation’s response, which he said was “proportionate and relevant.”

The United Nations agency moved to the top level of its pandemic alert following advice from a group of scientists and health officials who may have ties to the pharmaceutical industry, Sweden’s Svenska Dagbladet newspaper said last week, citing reports in Danish newspaper Information and the journal Science. WHO spokesman Gregory Hartl told the newspaper that the decision to declare a pandemic was made by Director General Margaret Chan alone.

‘Machine Grinding’

In July, epidemiologist Tom Jefferson told Germany’s Der Spiegel that WHO, public health officials, virologists and pharmaceutical companies may have had ulterior motives in promoting the pandemic threat.

“They’ve built this machine around the impending pandemic,” Jefferson was quoted as saying.

“There’s a lot of money involved, and influence, and careers, and entire institutions,” he said. “All it took was one of these influenza viruses to mutate to start the machine grinding.”

Public perceptions about the pandemic and national preparedness plans have been influenced since 2004 by the threat of bird flu, “widely regarded as the virus most likely to ignite the next influenza pandemic,” WHO said in a statement yesterday. The H5N1 strain of avian influenza killed 59 percent of the 444 people known to have been infected, according to WHO.

Adjusting Perceptions

“Adjusting public perceptions to suit a far less lethal virus has been problematic,” WHO said. “Given the discrepancy between what was expected and what has happened, a search for ulterior motives on the part of WHO and its scientific advisers is understandable, though without justification.”

Since April, at least 622,482 people have been infected with the virus in more than 207 countries and territories, according to WHO.

Swine flu infections and deaths reported to WHO are based on laboratory confirmed tests rather than mathematical modeling used to estimate fatalities from seasonal flu, the agency said.

“With the current pandemic, we really have data which is almost an anomaly, when we look at how influenza has been counted in the past,” Keiji Fukuda, WHO’s special adviser on pandemic influenza, told reporters on a conference call from London yesterday. “People do not typically count influenza deaths on a one-by-one basis. And so, we do not have a lot of data on laboratory-confirmed deaths for seasonal influenza.”

Accurate assessments of deaths and mortality rates will probably be possible only one to two years after the pandemic has peaked, WHO said.

“What we’re doing is reporting on the final score and we’re only at half time,” said Osterholm at the University of Minnesota. “We have no clue what’s going to happen in the next three to six months.”

To contact the reporter on this story: Jason Gale in Singapore at j.gale@bloomberg.net