Swine flu pandemic 'unstopable': WHO

A senior World Health Organization official said Monday that all countries will need access to vaccines against swine flu as the pandemic is "unstoppable," as researchers in the United States compared it to 1918 virus.

A group of vaccination experts concluded after a recent meeting that "the H1N1 pandemic is unstoppable and therefore all countries would need to have access to vaccines," said Marie-Paul Kieny, WHO director for vaccine research.

Health workers should be at the front of the line for vaccinations since they are required to keep health systems going while people continue to fall sick, she added.

Countries would be free to decide on their national priorities, but other groups should include pregnant women and anyone over six months-old who has chronic health problems.

The WHO official said a swine flu vaccine should be available as early as September.

A disturbing resemblance to the 1918 pandemic flu

The new H1N1 influenza virus bears a disturbing resemblance to the virus strain that caused the 1918 flu pandemic, with a greater ability to infect the lungs than common seasonal flu viruses, researchers from the University of Wisconsin reported on Monday.

Tests in several animals confirmed other studies that have shown the new swine flu strain can spread beyond the upper respiratory tract to go deep into the lungs -- making it more likely to cause pneumonia, the international team said.

In addition, they found that people who survived the 1918 pandemic seem to have extra immune protection against the virus, again confirming the work of other researchers.

"When we conducted the experiments in ferrets and monkeys, the seasonal virus did not replicate in the lungs," said Yoshihiro Kawaoka of the University of Wisconsin, who led the study. "The H1N1 virus replicates significantly better in the lungs."

The new swine flu virus has caused the first pandemic of the 21st century, infecting more than a million people, according to estimates, and killing at least 500.

Flu viruses change constantly, which is why people can be re-infected and why the vaccine must be changed regularly. Current seasonal strains of H1N1 are distant cousins of both the 1918 pandemic strain and the new H1N1 strain.