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Polio & Post-Polio Fact Sheet

Poliomyelitis and the epidemics

Acute poliomyelitis in the world today

The late effects of poliomyelitis


Poliomyelitis and the Epidemics

Poliomyelitis, a neuromuscular disease also known as infantile paralysis, is caused by the poliovirus of which there are three types. Infection occurs by fecal/oral contamination. The virus replicates in the gastrointestinal tract and is carried by the blood throughout the body. In 1%-2% of the infections, the poliovirus invades the nerve cells (motor neurons) of the spinal cord. When it does, muscles connected to the damaged or destroyed nerve cells can no longer properly function, resulting in weakness or paralysis of the limbs, and, possibly, the muscles controlling speech, swallowing, and breathing.

Poliomyelitis dates back to at least 1350 BC. Major epidemics occurred in Stockholm, Sweden (1887, 1905, 1911) and in Vermont, United States (1894). In 1916, the great New York epidemic killed 6,000 people and left 27,000 disabled. The number of cases reported during the '40s ranged from a low of 4,167 in 1942 to a high of 42,033 in 1949. The largest number of cases ever reported in the United States was over 58,000 in 1952.

The vaccine developed by Jonas E. Salk, using killed or inactivated poliovirus (IPV), was made available by injection in 1955. The oral polio vaccine (OPV), developed by Albert B. Sabin using the live but weakened poliovirus, was approved for use in 1962.

Acute Poliomyelitis in the World Today

As of August 2002, there were 483 confirmed cases of acute poliomyelitis reported to authorities worldwide. It should be noted that not every case is reported. The World Health Organization (WHO) target date for worldwide certification is 2005. Certification is the process that verifies that a region is polio-free. To date, the Region of the Americas (36 countries), the Western Pacific Region (37 countries and areas including China), and the WHO European Region (51 countries) have been certified polio-free. Acute poliomyelitis is now found only in parts of Africa and South Asia. A main resurgence of polio occurred in Northern India in late 2002 with 1,554 cases detected nationwide.

The last case of acute poliomyelitis in the Western Hemisphere caused by the wild poliovirus (that naturally occurs in the environment) was reported in Peru in 1991. During the last half of 2000, seven laboratory-confirmed cases of poliomyelitis were reported in the Dominican Republic and Haiti. The isolated virus is unusual because it was derived from the oral poliovirus vaccine (OPV). Mass vaccination campaigns have been conducted in both of these nations.

All of the new cases of poliomyelitis reported since 1979 in the United States have been caused by the oral polio vaccine (OPV), the "live" vaccine. The number of vaccine-associated cases confirmed in 1995, 1996, 1997, and 1998 was 6, 5, 3, and 1, respectively. As a result of these cases, The National Childhood Vaccine Injury Act of 1986 (PL-99-660) created a no-fault compensation alternative to suing manufacturers. The Centers for Disease Control and Prevention and the Federal Drug Administration developed a Vaccine Adverse Event Reporting System (VAERS) to collect data on the reactions to all vaccines.

In an effort to decrease the number of vaccine-associated cases of polio caused by an all-OPV schedule, the United States Advisory Committee on Immunization Practices (ACIP) changed its policy on polio vaccination in early 1997, and again, in June 1999. The recommended IPV-only immunization schedule took effect January 1, 2000. No cases of acute poliomyelitis have been reported in the United States since 1999.

The WHO recommends an all-OPV schedule in the mass campaign to eradicate the poliovirus from the world.

Denmark uses a sequence of IPV and/or OPV. France, The Netherlands, and Canada use IPV exclusively. Australia, Germany, New Zealand, Switzerland and the United Kingdom use the OPV (except for special cases).

Polio & Post-Polio Fact Sheet, continued ...