Vaccine
Immunity
Although
full immunity from vaccination does not last forever, some degree
of protection against death from the disease may last for many
years. The data published by Hanna in 1913 from an outbreak of
smallpox in Liverpool, England, in 1902 to 1903, illustrated the
ameliorating effect of childhood vaccination on the severity of
smallpox. (22:V2:29) There was a striking
difference between vaccinated and unvaccinated patients in all
groups, both in the spectrum of severity and in case-fatality rates.
Production decreased with age-with increasing intervals since vaccination-
but was substantial even in those aged more than 50 years.
Other studies
supported that vaccination had longer lasting effect than originally
thought. Data collected by Mack from Western countries with importations
of smallpox between 1950 and 1971 showed the case-fatality rate
was 52% in never vaccinated individuals, 1.4% in those vaccinated
0-ten years before exposure, and still only 11% in those vaccinated
over 20 years before exposure. (22:V2:30)
An attempt to
create an attenuated vaccine in Japan proved to have dramatic reductions
in adverse reactions. However, it was never able to be challenged
against naturally occurring disease, since eradication programs
were so successful. (22:V6:5)
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