What is the polio vaccine?

Definition

There are two types of polio vaccine: inactivated and oral, first available in 1955 and 1962, respectively. The vaccines provide immunity to poliomyelitis, or polio, a viral disease that damages nerve cells. The virus enters through the mouth and replicates in the intestines. It then enters the bloodstream and crosses into the central nervous system, where it attacks the nerve cells.

The first signs of polio are fatigue, headache, nausea, neck stiffness, and fever. Eventually, the nerves no longer send out electrical impulses to move muscles, and the body can become paralyzed; paralysis, however, is uncommon. The arms and legs are affected first, and in serious cases, the chest muscles are affected, resulting in respiratory failure.

Types

The inactivated polio vaccine (IPV), developed by Jonas Salk in the early 1950s, was the first polio vaccine available (1955). Salk based his vaccine, which is injected, on a then-new premise: that only the outer shell of the virus was needed to confer immunity. At the time, all vaccines were manufactured from live but weakened viruses.

In the late 1950s, Albert Sabin produced an oral form of the polio vaccine. Sabin’s oral polio vaccine (OPV), first administered in 1962, used a weakened form of the live poliovirus to stimulate antibody production. Decades earlier, Sabin proved that polio resides in the intestines rather than the nervous system, laying the theoretical groundwork for an orally administered vaccine. Once introduced, OPV quickly became the dominant polio vaccine because it was so easy to administer and it quickly conferred immunity.

The unique advantage of OPV is the use of live poliovirus. The virus, although weakened, is shed in feces from recently vaccinated persons. An unvaccinated person who comes in contact with the shed virus from a recently vaccinated person, for example, a parent who recently changed a baby’s diaper, may contract the weakened poliovirus and thus become passively vaccinated. This ability of OPV to confer immunity to persons not directly vaccinated helped spread immunity and helped eliminate outbreaks of polio.

Side Effects

Although the live virus contained in OPV is weakened, it is still a live virus
that can cause infection. In rare cases, OPV causes vaccine-associated paralytic
poliomyelitis, or VAPP. People vaccinated with OPV shed the weakened poliovirus up
to six weeks after each dose. Caregivers or others with a weakened immune system,
such as those who have had organ transplants or who have human immunodeficiency virus
(HIV) infection, may develop VAPP if they come in close
contact with newly vaccinated children.

The most common adverse events associated with IPV is soreness at the injection site. Allergic reactions, including respiratory difficulties, increased heart rate, hives, dizziness, or swelling of the throat, are rare.

Impact

Polio has no cure and can be prevented only through vaccination. Together, IPV and OPV eradicated polio from most of the world. Polio has become so rare in the United States that the small risk of VAPP associated with OPV is now greater than the benefit of passive immunization. IPV is now the recommended vaccine for all children. Recommendations require three injections for infants at two, four, and six months of age, between six and eighteen months of age, and booster shots between four and six years of age.

Bibliography

Bruno, Richard L. The Polio Paradox: Understanding and Treating “Post-Polio Syndrome” and Chronic Fatigue. New York: Warner, 2002. Print.

Naden, Corinne J., and Rose Blue. Jonas Salk: Polio Pioneer. Brookfield: Millbrook, 2001. Print.

Offit, Paul A. The Cutter Incident: How America’s First Polio Vaccine Led to the Growing Vaccine Crisis. New Haven: Yale UP, 2005. Print.

Strauss, James, and Ellen Strauss. Viruses and Human Disease. 2nd ed. Boston: Academic Press/Elsevier, 2008. Print.

Wagner, Edward K., and Martinez J. Hewlett. Basic Virology. 3rd ed. Malden: Blackwell Science, 2008. Print.