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1.4 How effective is vaccination at producing immunity?




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This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax lynng@alsirat.com with numerous contributions by others.

1.4 How effective is vaccination at producing immunity?

Vaccination does not always work. For one thing, vaccines can lose
effectiveness when they aren't stored properly. And even if they are
stored effectively, they will fail to stimulate immunity a certain
percentage of the time. The effectiveness of vaccines varies,
depending on the vaccine. Effectiveness can also vary depending on the
age, sex, and health of the recipient. Sometimes different strains of
a vaccine can have different effectiveness.

Vaccine effectiveness is measured in two ways. First, antibody levels
are measured after a vaccine is given. Second, people are vaccinated
and then followed to see whether they get the disease when they are
exposed to it. Estimates of effectiveness can vary in some cases
depending on the level of antibodies which is considered as passing,
and the criteria for measuring whether someone has the disease (for
instance, pertussis vaccine is more effective at preventing full-blown
pertussis than at preventing a mild cough). Also, some sources give
estimates of field effectiveness which take into account difficulties
in storing vaccines in some areas; these estimates tend to be lower
than estimates based on studies of vaccination in the US or other
developed countries.

Estimates of effectiveness of individual vaccines are given in the
section for each vaccine (and, where I have found variations in
estimates of effectiveness, I have noted that as well).


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From J Thompson (jet14@columbia.edu):

In addition to all of the factors you mentioned which determine the
variability of response to a vaccine, another very important factor is
the genetic inheritance of every individual. To give an example I feel
sure of, I'll use the Hepatitis B vaccine. A certain small percentage
of the population has no response at all to the recombinant Hep B
vaccine. This occurs because these people lack the particular forms of
major histocompatibility complex (MHC) proteins which are necessary to
"present" the _single_ protein in the vaccine to the immune
system. These people can make a good response to the whole virus, but
they have a problem with the protein in the vaccine.

This also highlights the need for "herd immunity," since people who
cannot make an immune response to a vaccine component will _never_
have a good response to the vaccine, regardless of how often it is
given.
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