The flu that killed 50 million a century ago is appearing

The US Agency for Disease Control and Prevention (CDC) has warned of the spread of an influenza strain that, in 1918, had turned into a pandemic having killed 50 million people in two years.

The strain known as H1N1 has re-emerged this season, said a CDC spokeswoman at Salon.

Kristen Nordland said the last four weeks had seen another H3N2 virus spread in the southwestern states. Seven people died from a combination of strains H1N1, H3N2 and B.

Nordland has ruled out swine flu becoming a deadly pandemic, as it was a century ago. With influenza viruses constantly changing, this year's H1N1 strain is not the same as the H1N1 virus a century ago, she said.

Influenza viruses result from genetic mutations and the fusion of strains, making them resistant to drugs. But in the case of the H1N1 flu, multiple changes in the virus reduce the risk of a pandemic.

Nordland said the vaccines and available drugs included pharmaceutical components designed to counter the H1N1 strain, including Flumadine and Tamiflu.