Poliomyelitis (polio) is a highly infectious disease caused by a virus. It invades the nervous system, and can cause crippling paralysis, sometimes in a matter of hours. Polio generally affects children under the age of three, but adults can contract it as well.
The virus enters the body through the mouth and multiplies in the intestine. Initial symptoms include fever, weakness, headache, vomiting and pain in the limbs. A lifelong paralysis can set in quickly. Among those paralyzed, 5%-10% die when their breathing muscles become immobilized. Many of those infected with the virus will show no symptoms at all but can pass the virus on to others.
Polio is incurable but it can easily be prevented through immunization. Polio vaccine, given multiple times, almost always protects a child for life. Through quality vaccination and disease-reporting (surveillance) systems, the Western Pacific Region has been polio-free since 19 March 1997 when the Region’s last case caused by an indigenous (locally circulating) poliovirus was reported in Cambodia. Polio continues to occur in other parts of the world.
Once established in the intestines, poliovirus can enter the blood stream and invade the central nervous system—spreading along nerve fibres. As it multiplies, the virus destroys nerve cells (motor neurons), which activate muscles. These nerve cells cannot be regenerated and the affected muscles no longer function. The muscles of the legs are affected more often than the arm muscles. The limb becomes floppy and lifeless - a condition known as acute flaccid paralysis (AFP).
Surveillance for polio is based on surveillance for AFP in children under age 15. Stool specimens have to be tested for poliovirus at a quality laboratory, accredited under WHO standards. AFP surveillance results are regularly reported to WHO and quality standards are applied to ensure that almost all AFP cases are investigated and polio would not be missed.
Two types of vaccine against polio are available. The first is a live attenuated (weakened) oral polio vaccine (OPV), which was developed by Dr Albert Sabin in 1961. OPV is given orally and its action is two-pronged: OPV produces antibodies in the blood ('humoral' or serum immunity) to all three types of poliovirus. In the event of infection, this will protect the individual against polio paralysis by preventing the spread of poliovirus to the nervous system. OPV also produces a local immune response in the lining ('mucous membrane') of the intestines—the primary site for poliovirus multiplication. The antibodies limit the multiplication of 'wild' (naturally occurring) virus inside the gut, preventing effective infection.
The unique ability of OPV to induce this intestinal, local immunity is probably responsible for the extraordinary effect of OPV mass campaigns in interrupting wild poliovirus transmission. Due to these advantages, OPV remains the vaccine of choice for the eradication of polio.
The second type, the inactivated polio vaccine (IPV), was developed in 1955 by Dr Jonas Salk. IPV is used primarily in countries where the wild poliovirus has already been eliminated. It has to be injected by a trained health worker.
WHO recommends that polio vaccine be given at birth (in areas where polio is still endemic), at six weeks, 10 weeks and 14 weeks.
The Global Polio Eradication Initiative, spearheaded by national governments, Rotary International, the United States Centers for Disease Control and Prevention (CDC), UNICEF and WHO, is the largest public health initiative the world has ever known. In the Western Pacific, the Governments of Australia and Japan provide significant support beyond their own national programmes.