> Date:    Sat, 24 Mar 2001 12:41:00 -0500
> From:    Jodi Barnard
> Subject: Re: Daycare Germs
>
>   Her response was that it was nothing to worry
> about and that having been exposed to colds as an infant would make
> her less suseptable to being ill once in school.  Her reasoning was
> that she would
> have already been exposed to the common cold viruses and would be less
> likely to fall ill with the same stings of the viruses having built up
> a
> stonger immune system.

The problem with this reasoning is that, while it does apply in some
cases (ie: once you have chicken pox, you rarely get it a second time)
it does not apply in all cases.  This is because the viruses which cause
colds are constantly undergoing new mutations and antigenic shifts,
creating new strains of virus which we are *not* immune to, even if we
had last year's version.  Sure, you won't catch the same strain if it
goes around again, but there are new strains all the time.

Consider influenza.  Just because you had it last year or you were
immunized last year does not mean that you will be protected this year.
A new influenza vaccine is produced each year, to protect against the
strains predicted for that season.  This same process of mutation/shift
occurs in other viruses as well.  So, having had colds in previous
seasons does NOT necessarily protect from future colds.  This is a very
attractive and popular idea (understandably) but it is not accurate.
Note however, that this discussion differs from the one about 'donkey
dung'.  While we may need exposure to antigens for proper immune system
development, being sick a lot in infancy and childhood doesn't
necessarily mean we'll be 'immune' to illness when we get older.

Catharine Decker, MD

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