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VOL. 71 (2), 321-339, 2005 HISTORY AND FUTURE OF POLIOVACCINATION...

Another break-through was the result of a collaborative effort of
many investigators (Committee on Typing of National Foundation
of Infantile paralysis, 1951). This study showed that polioviruses
belong to only three distinct serological types (type 1 to 3).

Due to this new knowledge on poliovirus and poliovirus
replication, the fifties (of the 20th century) evolved into the golden
age of poliovaccin development. Two different kinds of vaccine
became available. Describing the detailed history of the development
of both vaccines could be the subject of another topic. Therefore,
only the vaccines will be described, together with their advantages
and disadvantages.

The first vaccine developed in 1955 by Dr. Jonas Salk (10, 11),
was a formalin inactivated (killed) poliovaccine (IPV). The vaccine
contains neurovirulent virus from three different strains (of three
different serotypes), originally grown on primary cells of monkeys.
After sufficient growth, the virus is concentrated, purified and
inactivated with formaldehyde. Each dose of vaccine contains 40 D
antigen units of type 1, eight D antigen units of type 2 and 32 D
antigen units of type 3. Trace amounts of antibiotics are also found
in the vaccines (neomycin, streptomycin, etc.). Some manufacturers
use 2-phenoxyethanol as a preservative (12).

IPV needs to be injected and works by producing protective
antibodies in the blood (serum immunity) – thus, in fact, preventing
the spread of poliovirus to the central nervous system. However, it
induces only very limited levels of poliovirus inside the gut. As a
result, it provides individual protection against polio paralysis but,
unlike OPV, cannot prevent the spread of wild poliovirus.

There are several advantages of using IPV: (1) IPV is not a «live»
vaccine, consequently IPV carries no risk of vaccine-associated polio
paralysis, (2) it is more heat stable than OPV, and (3) immunization
with IPV triggers an excellent response of the immune system in
most IPV recipients.

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