The H1N1 flu pandemic is moderate but infects and sometimes kills much younger people than traditional seasonal influenza, the World Health Organization (WHO) said on Tuesday.

Comparing the number of deaths from the pandemic virus known as swine flu with those from seasonal influenza can be misleading, the U.N. agency said.

WHO continues to assess the impact of the influenza pandemic as moderate, it said in a statement. Accurate assessments of mortality and mortality rates will likely be possible only one to two years after the pandemic has peaked.

The H1N1 virus has killed at least 10,582 people worldwide since emerging in April, but these are only laboratory-confirmed cases. Testing is costly and demanding, and many poor countries fail to investigate the cause of death as fatalities from respiratory diseases including pneumonia are common, it said.

For several reasons, these numbers do not give a true picture of mortality during the pandemic, which is unquestionably higher than indicated by laboratory-confirmed cases, the WHO said.

Seasonal flu kills 250,000 to 500,000 people a year globally, but this is an estimate derived from statistical models.

WINTER MONTHS

The models use data from death certificates and medical records on mortality from all causes to calculate so-called excess mortality that occurs during a period when influenza viruses are circulating widely in winter months, the WHO said.

During epidemics of seasonal influenza, around 90 percent of deaths occur in the frail elderly, who often suffer from one or more chronic medical conditions, it 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, it added.

The WHO also said it would send H1N1 vaccine to Azerbaijan and Mongolia by year-end, the first of 95 countries which it aims to supply with enough doses for 10 percent of their population over the next months.

Before the end of the year, Azerbaijan and Mongolia will likely be receiving vaccine, WHO spokesman Gregory Hartl told a news briefing in Geneva.

Afghanistan is also in line to receive supplies soon.

Health care workers followed by people at risk are the top priority for receiving vaccine. Initially it is sending enough doses for about 2 percent of a needy country's population.

It is most important to ensure that health systems have enough resources and that emergency services and intensive care units continue to function, Hartl said.

Medicine