Medical advances such as ventilators and intensive care were not available during previous pandemics. (CBC)

The strain of swine flu virus currently circulating around the world is less deadly than previously thought, say British scientists who compared its effect to that of other pandemic viruses.

The 2009 flu pandemic is about 100 times less lethal than the 1918 Spanish flu and nearly 10 times less fatal than the flu pandemics of 1957 and 1968.

Those findings were reported in Thursday's online issue of British Medical Journal, BMJ.

After analyzing British health department data on all reported swine flu patients who were hospitalized between July and Nov. 8 , the researchers estimated that about 26 of every 100,000 people infected with the H1N1 influenza A virus that causes swine flu died. That is a death rate of 0.026 per cent.

The findings are similar to a U.S. study published on Monday that estimated the death rate in the current swine flu pandemic is 0.048 per cent, or one death per every 2,000 cases.

"The first influenza pandemic of the 21st century is considerably less lethal than was feared in advance," England's chief medical officer, Liam Donaldson, and his co-authors from Britain's Health Protection Agency wrote in the study.

In comparison, the fatality rate for the 1918 Spanish flu pandemic was two to three per cent, compared with around 0.2 per cent for the pandemics in 1957-1958 and 1967-1968. Fatality estimates for previous pandemics were probably less reliable since they were based on statistical methods and death certificates, with few — if any — lab confirmations.

Since the past pandemics, there have been advances in medicine such as ventilators to help patients with breathing problems, as well as better housing, health care and nutrition, Donaldson said.

When the World Health Organization declared swine flu had reached a pandemic stage in June, the agency described it as "moderate," with most people infected showing mild symptoms and recovering without medical treatment.

A pandemic designation reflects how widely a virus has spread, not the severity of illness.

Findings not a reason for inaction

Donaldson's study suggested two-thirds of those who died from H1N1 would be eligible for the H1N1 vaccine under the British government's plan, which prioritizes those at highest risk of developing complications from the flu.

This includes patients sick in hospital, pregnant women, people with asthma or other underlying health problems and health care workers.

"Viewed statistically, mortality in this pandemic compares favourably with 20th century influenza pandemics. A lower population impact than previous pandemics, however, is not a justification for public health inaction," the study's authors concluded. "Our data support the priority vaccination of high-risk groups."

Some of the deaths, 38 per cent, occurred in people not considered at high risk.

The findings also reinforced calls to prescribe antiviral medications for people at high risk or those showing severe symptoms.

Most of the people who died of swine flu in Britain, 78 per cent, had been prescribed antiviral drugs. But of these, 76 per cent did not received them within the first 48 hours of illness as recommended.

Infection rate higher among native populations

Also on Thursday, U.S. health officials said an estimated 15 per cent of Americans had been infected with the H1N1 virus by mid November.

In its weekly report on death and disease, the U.S. Centers for Disease Control and Prevention (CDC) suggested the death rate among the aboriginal population in the U.S. is about four times higher than that of all other racial and ethnic groups combined.

Similarly, indigenous populations in Australia, Canada and New Zealand have been found to have a three to eight times higher rate of hospitalization and death associated with swine flu.

There is a lot of debate about why the rates are higher among aboriginal populations, but it likely reflects environmental conditions such as nutrition in early childhood, access to health care and the a higher likelihood of underlying disease such as diabetes and asthma, said CDC director Dr. Thomas Frieden.

With files from The Associated Press