Flu vaccine problems

Jay Mone jaymone at paonline.com
Sun May 7 20:50:32 EST 2000

Suppose that you are infected with an influenza A virus.  You begin to mount
an immune response against this particular virus strain.  If you are then
infected with an immunologically cross reactive virus, you will already be
plugged in to an ongoing response.  If you are infected by this second
strain after your prior response is finished, you will activate memory cells
from the previous infection, as well as mount a primary response to the new
viruses epitopes.  This is why epidemics decrease in severity even as the
flu virus antigenically drifts, and is eventually replaced by a new virus,
usually every 10-20 years or so.  As more people become infected, they are
usually partially protected from infection by related viruses, and if
disease develops, it is often less severe.
Influenza A has an enormous capacity to drift antigenically.  It is
interesting to note that in their normal reservoir (ducks etc.), influenza
A hasn't changed at all in 40 years.  It appears that an evolutionary stasis
has occurred and the virus and host are perfectly adapted.  The same is seen
with simian immunodeficiency viruses in their normal hosts.

Jay Mone'

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