Re: Why do we have to get a flu shot every year?

Hello,

   The main reason that we need to get flu shots every year is that the 
influenza virus changes from year to year.  The immune system sees the 
surface of the virus, the coat, and the influenza virus is smart and changes 
its coat from year to year, rendering the immune response to the old coat 
useless (1).  It's a little bit like HIV, which constantly mutates to avoid 
the attacks of the immune system.

   The makers of the influenza vaccines on the market predict what strain(s) of 
virus will cause this year's round of flu and include the coats of those in 
the vaccine.  It's complicated, though, because not only does the virus 
change its coat often, it also has lots of strains, which are perceived as 
different by the immune system (1,2).  As you know, influenza causes lots of 
illness and even deaths each year, especially in the elderly and in small 
children, both through its initial infection and the pneumonia that the 
virus opens the door to (3), so it is important for the vaccine makers to 
predict correctly and for at-risk populations to get vaccinated.

   So, for now, we are stuck with getting a vaccine every year.  In order to 
avoid having multiple yearly vaccinations, we must find a portion of the flu 
virus coat that doesn't change from year to year, and convince the immune 
system to attack that.  Researchers reported in the October issue of Nature 
Medicine that they may have found such a molecule.  It is called M2, and it 
is nearly invariant in all influenza A strains (2).  The existence of such a 
molecule gives hope that we will see a one-shot flu vaccine in the near 
future. 

   I hope that I have answered your question.  If I have not, or if you have 
more questions, please feel free to drop us a line.

Take care-
Ingrid Dodge

References:

1. Ben-Yedidia et al, International Immunology 11(7):1043-1051, 1999 Jul.
2. Neirynck et al, Nature Medicine 5(10):1119-1120, 1999 Oct.
3. Frace et al, Vaccine 17(18): 2237-2244, 1999 May 4.