How a Seasonal Flu Shot May Help You Battle Swine Flu

Information from the US Armed Forces shows that having a seasonal flu vaccination cuts the cost of swine flu by 45%; the overall risk of developing swine flu is cut by 42% and the risk of hospitalization by 62%.  On further analysis, it seems not everyone is protected.  Seasonal flu vaccine wasn’t effective in personnel aged 25-39, but it was effective (50-55%) in those under 25 or over 39.

What’s the explanation?  It’s been shown that people given seasonal flu vaccine don’t develop antibodies to H1N1 swine flu virus.  But antibodies are only one arm of the immune system – the other is ‘cell-mediated immunity’, where T-cells learn to recognize pathogens like the virus.  The next exposure to T-cells causes them to kill the invading virus, limiting the extent of the infection.  So seasonal vaccine provides partial immunity to swine flu. 

But why doesn’t this happen in the personnel aged 25-39?  Because, apparently, H1N1 viruses didn’t circulate from 1958 through 1978, so this the T-cells in people born during these years weren’t ’primed’ by a flu infection.

In fact, the more vaccinations or natural infections you have with different kinds of flu viruses, the better.  So it’s advisable to have a seasonal flu vaccination every year; next year, or the year after, the seasonal vaccine will probably contain specific protection against swine flu, but that isn’t essential to get a degree of protection from other H1N1 vaccines.