Paralytic poliomyelitis, or polio, is a neurological
disease caused by the enterovirus known as poliovirus. It is transmitted
through stool with an incubation period of 5-35 days, averaging 7-14 days,
and is more common in the summer and fall in temperate climates. About 95
percent of infections are asymptomatic. Paralytic polio represents only
0.1% of all cases.
Paralytic polio affects the nuclei of cranial nerves (bulbar polio) and
the anterior motor neurons of the spinal cord (spinal polio).
Bulbar polio results in double vision, facial weakness, difficulty
talking, nasal voice, weakness of the neck muscles, difficulty in chewing
and swallowing, and even regurgitation of fluids through the nose. There
may be loss of the gag reflex necessary to protect the airway, pooling of
secretions, tongue deviation, and associated respiratory paralysis.
Spinal polio usually results in an asymmetric paralysis of the arm and
leg muscles, and may involve muscles of the bladder and respiratory
system. Diagnosis is usually confirmed by viral culture of stool specimens
and throat swabs.
Some of the complications include pneumonia, urinary tract infections,
emotional problems, persistent paralysis, shock, the post-polio syndrome
(characterized by muscle pain, exacerbation of weakness and/or new
paralysis) and even death.
In order to prevent polio, two types of vaccines were developed -- a
live oral vaccine (OPV) developed by Dr. Sabin and an inactivated
injectable vaccine (IPV) developed by Dr. Salk. The current oral vaccine
is a live, attenuated, trivalent virus vaccine that offers the benefits of
easy administration, local gastrointestinal immunity and secondary spread,
or herd immunity, through shedding into the intestinal tract. However, it
also carries the risk of vaccine associated paralytic polio (VAPP), which
occurs in one case per 2.4 million doses given. This risk is highest after
the first dose - approximately one case per 760,000 doses given.
Since 1979 there have been no cases of indigenous wild-type polio in
the United States, but there have been 144 cases of polio associated with
OPV use. The likelihood of someone bringing the wild-type poliovirus back
into the United States has substantially decreased due to the global polio
In 1997, in order to decrease the risk of VAPP but continue the
benefits of OPV, the Advisory Committee on Immunization Practices (ACIP)
recommended giving the inactivated polio vaccine (IPV) for the first two
immunizations followed by OPV for the third dose and subsequent booster
prior to starting school. The only disadvantage to IPV is that it involves
a shot, however, no declines in childhood vaccination coverage have been
observed despite the need for additional injections.
In order to eliminate the risk for VAPP, the ACIP is now recommending
an all-IPV regimen for routine childhood vaccination in the United States.
All children should receive a total of four doses of IPV at ages 2 months,
4 months, 6-18 months, and 4-6 years.
OPV should only be used in unvaccinated children who will be traveling
in less than 4 weeks to areas where polio is endemic; in mass vaccination
campaigns to control outbreaks of paralytic polio; and in children of
parents who do not accept the recommended number of vaccine injections. In
this latter group, OPV should be used only for the third and fourth doses
and only after the risk for VAPP is discussed with the parent or
19 November 1999
Last updated 19 November