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

nervous system. But, OPV also produces a local immune response in
the mucous membrane of the intestines (which is in fact the primary
site for poliovirus multiplication). The antibodies limit the
multiplication of «wild» or «neurovirulent» virus inside the gut,
preventing effective infection. This intestinal immune response to
OPV is probably the main reason why mass campaigns with OPV
can rapidly stop person-to-person transmission of wild virus.

What are the main advantages of OPV? (1) OPV is a cheap
vaccine. This is due to the fact that it is an orally applicable vaccine.
It can be given by volunteers (see National Vaccination Days) and
—unlike most other vaccines— does not require sterile injection
equipment. (2) The short-term shedding of vaccine virus in the
stools of recently immunized children, means that in areas where
hygiene and sanitation are poor —and the incidence of poliovirus
is likely to be high— immunization with OPV can result in the
«passive» immunization of persons with close contact. As discussed
above, the unique ability of OPV to induce intestinal immunity is
probably responsible for the extraordinary effect of OPV mass
campaigns interrupting wild poliovirus transmission.

OPV has also some disadvantages: (1) although OPV is safe and
effective, it can induce poliovirus paralysis, the so-called vaccine-
associated infection in approximately 1 in every 2.5 million doses.

THE CONTROL OF POLIOMYELITIS

Due to mass immunization campaigns with IPV in the second
half of the fifties of the 20th century in the U.S.A. and in Europe, the
incidence of poliomyelitis in both regions dropped dramatically. In
1962, IPV is replaced by OPV in much countries. OPV is shown to
be superior in terms of ease of administration, but also provides
longer-lasting immunization. Using OPV, several countries appear to
interrupt transmission of poliovirus after introducing OPV. But also
in countries where IPV is used, such as Sweden, Finland and the
Netherlands, the potential of IPV for controlling poliomyelitis is
amply illustrated. By the 1970s poliomyelitis is no longer a threat in
most developed countries (1, 8).

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