The influenza virus can go from humans to pigs to birds (ducks etc) and back. Usually between species it mutates or changes. Every 7 years or so there are significant changes, with major changes every 21 years. Another problem is there are many varieties and each year a few become dominant among humans. The CDC screens the dominate strains in the population and picks the top 3 to make the new vaccine each year (they're doing it for 2013 fall flu season as we speak). So a few years ago H1N1 was the biggie , now I think it's H2N5. Next year?? who knows? A minor flu outbreak like we have now can cost us about $20-25 billion in medical bills and lost business productivity. A major one even more ! So not only from a public health standpoint but just from the economics, you can see how important it is to keep this controlled. Your tax $ at work at CDC.
Where do they get their names? The H stands for hemagglutinin, and N - neuraminidase. These are 2 antigens (proteins) that are on the surface of the virus. Hemagglutinin causes RBCs to clump. Neuraminidase breaks down tissue chemicals and helps it to spread. The mutations constantly occur in these 2 antigens.
If you get vaccinated with H1N1, the antibodies you make will NOT protect you from H2N5 virus... this is why people should get a new shot each year... either the virus or the dominant strain changes and likely last years vaccine won't protect you if this happens (highly likely). IF you get vaccinated you make antibodies that attach to the H & N proteins and block attachment to your cells. IF the virus can't attach, they can't infect, and can't replicate to make you sick !
Historical fact: An estimated 20 million people died in the 5 years of WWI. In 1918 – 1919 there was a flu epidemic that killed 30-40 million people around the world. One of the largest pandemics in history. It rivaled the plague pandemics of the 1300s !! More people died of the flu those 2 years than in the 5 of WWI !!
BTW I love the drive through vaccination program (above).. gives new meaning to "drive by shotting" !!
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