Polio vaccine
The polio vaccine is a crucial medical advancement designed to prevent poliomyelitis, a viral disease that can lead to paralysis by damaging nerve cells. There are two primary types of polio vaccines: the inactivated polio vaccine (IPV) and the oral polio vaccine (OPV). IPV, developed by Jonas Salk and first introduced in 1955, is administered via injection and uses the inactive form of the virus to stimulate immunity. On the other hand, the OPV, created by Albert Sabin and introduced in 1962, employs a weakened live virus that can be taken orally, proving easier to administer and fostering herd immunity as vaccinated individuals can shed the virus.
While both vaccines have significantly contributed to the near eradication of polio, OPV carries a small risk of vaccine-associated paralytic poliomyelitis (VAPP) in rare cases. Consequently, IPV is now the preferred choice in many countries, particularly in the United States. Vaccination regimens typically recommend a series of doses during infancy and early childhood to ensure comprehensive immunization. The global impact of these vaccines has been profound, with polio eradicated in most regions by 2022, leaving only a few countries with ongoing transmission.
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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 event 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. By 2022, according to the World Health Organization, polio had been eradicated from every country in the world, with the exception of Pakistan and Afghanistan. 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. Warner, 2002.
Naden, Corinne J., and Rose Blue. Jonas Salk: Polio Pioneer. Millbrook, 2001.
Offit, Paul A. The Cutter Incident: How America’s First Polio Vaccine Led to the Growing Vaccine Crisis. Yale UP, 2005.
"Polio Vaccination." CDC, 9 July 2024, www.cdc.gov/polio/vaccines/index.html. Accessed 12 Dec. 2024.
“Poliomyelitis (Polio).” World Health Organization (WHO), who.int/health-topics/poliomyelitis#tab=tab‗1. Accessed 12 Dec. 2024.
Strauss, James, and Ellen Strauss. Viruses and Human Disease. 2nd ed., Academic Press/Elsevier, 2008.
Wagner, Edward K., and Martinez J. Hewlett. Basic Virology. 3rd ed., Blackwell Science, 2008.