Swine flu closely related to 1918 Spanish flu pandemic

Mar 25 2010

By Candy Lashkari

In research on the swine flu virus it has been seen that the virus may seem new, but it has old relatives. An influenza virus which was pandemic in 1918 is seen to be very closely related, structurally speaking, to the H1N1 swine flu vaccine. This virus has the dubious distinction of having claimed between 40 million to 100 million lives in the flu wave of 1918.

In a statement issued by Dr. Anthony Fauci said "This study defines an unexpected similarity between two pandemic-causing strains of influenza." Dr Anthony Fauci is the director of the National Institute of Allergy and Infectious Diseases. The pandemic strains differ in their amino – acid sequences between 30 to 58% in 9 strains of seasonal flu viruses dating from 1977 to 2007.

Two studies have shown that the structural element called hemagglutinin is quite similar in the two distant cousins. It is the hemagglutinin that the virus uses to infect cells and is also responsible for the “H” designation given to the influenza viruses.

In one study which was published by Science Translational Medicine, the vaccine developed for the 1918 virus was injected in mice by Chih-Jen Wei, Gary Nabel and colleagues at NIAID. When subsequently infected by the HINI swine flu virus, the mice survived while unprotected mice died. When the reverse was tried and the swine flu vaccine was given to the mice before being infected by the 1918 virus, the same results were found.

"This is a surprising result," Gary Nabel said. "We wouldn't have expected that cross-reactive antibodies would be generated against viruses separated by so many years."

This may also be the reason why the elderly were not as susceptible to the H1N1 Swine flu virus as younger children were. Exposure to influenza strains before builds the body resistance to new strains as well.

The results of this research will come in handy when new vaccines are to be developed. "It gives us a new understanding of how pandemic viruses evolve into seasonal strains, and, importantly, provides direction for developing vaccines to slow or prevent that transformation," said Fauci.