Polio is an infectious disease caused by a virus spread through contact with infected persons, consuming contaminated food or by inhalation. It affects the central nervous system and can result in paralysis or death. There were polio epidemics in the United States during the '40's and '50s, and the first vaccine became available in 1955. Today polio is nearly unheard of in the United States but is still a problem in some developing countries. There are two kinds of polio vaccines. One is a weakened version of the virus and is given orally; the other consists of a killed virus and is given by injection.
Oral Polio Vaccine
According to the Case Western Reserve University Engineering and Science Review, polio virus invades through the nose or mouth, grows in the intestine, then travels through the bloodstream to the brain or spinal cord. The oral vaccine is made from weakened strains of the virus. It stimulates antibody production in the intestines and an immune response in the nose and mouth.
The oral vaccine is no longer common in the United States. It has been replaced by a series of four injections of a vaccine made from dead polio virus. The injected vaccine stimulates antibodies in the blood. Children usually receive the injections by the time they start school.
Benefits
According to The Children's Hospital of Philadelphia Vaccine Education Center, the oral vaccine stimulates an immune response in the nose, mouth and intestines, which stops the virus before it can invade the blood. Also, because it passes in its weakened form through the immunized person's stool, other persons can come in contact with it and become immunized too. This is an advantage in areas where the disease is still endemic. Finally, it is easier to administer in oral form, especially to children.
Risks
In rare cases, the oral vaccine itself can cause the disease. According to The Children's Hospital of Philadelphia Vaccine Education Center, approximately one in 750,000 people are paralyzed after taking the oral vaccine. By 1979 polio was virtually eliminated from the United States. There have been six to eight cases each year since then, and all were caused by the oral vaccine. The oral vaccine also can present a problem to immunocompromised people in contact with a vaccinated person.
Uses
Drugs.com explains that the oral vaccine is still used in special cases. It may be given to children who have not received any of their polio injections and are traveling to areas of the world where polio is still endemic. It also may be given to children whose parents do not want them to have all the injections. The children would receive the first two injections in the series, then are given the oral vaccine instead of the remaining two injections. It can be used when there are polio outbreaks and large numbers of people need to be quickly vaccinated. And it is used for people who have serious allergic reactions to the injected vaccine.
