Vaccinations: What are the risks?

ryan at ryan at
Mon Jun 12 14:58:45 EST 1995

In article <3rf1d0$prj at>, robison at (Keith Robison) writes:
> Arthur Flatau (flatau at dalhart) wrote:
> : >>> On Fri, 9 Jun 1995 17:27:27 GMT, M_Doherty at (M. Doherty) said:
> : I see no reason to immunize my children against chickenpox (this is
> : academic as they just had it).  I think it is reasonably likely that
> : routine immunization of children for chickenpox will just increase the
> : number of adults that get it, where it is much more serious.
> Can anyone explain this seeming non-sequitur?  If people are 
> immunized as kids and the protection is permanent, then
> they won't be able to get it as adults.  Even if the protection
> isn't permanent, won't immunizing children significantly reduce
> the available reservoir of chicken pox virus?  
> Keith Robison
> Harvard University

The enhanced risk of infection is to nonimmune adults in the same household as
the recently-immunized kids. When given a _live-virus_ vaccine (virus in the
shot can infect, replicate, be excreted as in normal infection; just causes no
disease symptoms or very mild symptoms) the vaccine-strain virus is shed
normally by the vaccinated kids. I think A. Sabin's concept of developing herd
immunity actually relied on kid-to-kid transmission of live vaccine-strain
virus, to immunize those not actually given the virus-containing shot/
sugar cube/whatever. I believe the risk of disease in adults infected by virus
excreted from vaccinated kids depends on the probability of the vaccine strain
virus reverting (mutating during replication in the vaccinated kid) to a more
pathogenic phenotype. This tendency to revert is a fundamental aspect of
vaccine safety, and is examined at length prior to general use of a 
live-virus vaccine.

With killed-virus vaccines this is usually not an issue. There have
been isolated cases of  commercial vaccine batches (I think in the earliest 
days of commercially-produced Salk-type polio vaccine) where incompletely-
killed virus preparations led to disease in vaccinees. These tragic incidents 
led directly to the more reliable tests of vaccine safety commonly in use today.

	Kevin W. Ryan
	Department of Virology & Molecular Biology
	St. Jude Children's Research Hospital
	Memphis, Tennessee 38101-0318, U.S.A.
	phone: (901) 522-0411
	fax:   (901) 523-2622
	Internet: ryan at

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