Before the polio vaccine was licensed in 1955, polio
disease was rampant in the United States and other developed
countries. In 1952 alone, polio left more than 20,000 Americans
paralyzed. By 1965, the number of Americans paralyzed from polio each
year had dropped to 61. Thanks to the vaccine, since 1979 not a
single case of natural, or wild, polio has been contracted in the
United States. Since 1991, not a single case of wild polio has been
contracted in the entire Western Hemisphere.
Polio infection is most common among children, but
infected adults are more likely to be paralyzed by the disease. Also,
while polio kills 2 to 5 percent of children afflicted by the
disease, it kills 15 to 30 percent of affected adults.
Polio has maimed and killed humans through the
centuries. Even drawings from ancient Egypt depict humans who appear
to have the withered limb of polio. If polio has been around for that
long, why did polio epidemics start in Europe in the early 1800s and
worsen in developed nations over the next hundred years? One theory
is that polio outbreaks occurred because sanitary conditions
improved.
Two hundred years ago, nearly all infants were
exposed to poliovirus when they still had some of their mother's
antibodies in their bloodstreams. Their immunity to poliovirus was
boosted as they were exposed over and over, throughout life, so the
proportion of people who were paralyzed by the disease was relatively
low. As sanitary conditions improved, infants were less likely to be
exposed to the virus. Older children and adults being exposed for the
first time were more likely to develop paralytic disease.
By the early 1950s, an average of more than 20,000
persons contracted paralytic polio in the United States each year.
Parents were terrorized by the fear of polio.
No wild polio has originated in the United States
since 1979, but five cases were imported between 1980 and 1989.
Outbreaks of polio continue to occur in sub-Saharan Africa, India,
and the countries contiguous with India.
Polio has been one of the most scrutinized vaccines
for two reasons. First, polio has almost been eradicated from the
globe, so many parents ask why the vaccine is needed at all. Although
we are close to global eradication, worldwide there were still
several thousand cases of polio in 1999, and the virus is easily
imported and spread. Until the world is polio free, we should keep
all peoples of the world vaccinated so we don't lose ground in the
eradication effort.
Second, until recently the U.S. (in accordance with
World Health Organization recommendations) relied primarily on oral
polio vaccine (OPV). This vaccine, containing live, weakened
poliovirus, is highly effective, but it actually caused some cases of
polio. So as of January 2000, OPV is no longer recommended except in
limited situations. Instead, inactivated polio vaccine (IPV), the
shot containing killed poliovirus, is recommended for the full
series.
