Poliomyelitis is a vaccine-preventable disease caused by the poliovirus.

This virus is highly infectious, spreading from person to person mainly through the fecal-oral route. Children under the age of 5 are most commonly infected. Seventy-two percent of infected children will remain asymptomatic but continue to shed the virus that may infect others. Once ingested, the virus multiplies in the gastrointestinal (GI) tract and can ultimately lead to an acute nonspecific illness including symptoms such as:

• Sore throat
• Vomiting
• Fever
• Fatigue
• Headache
• Neck stiffness
• Extremity stiffness/pain

Most notably, the virus’s invasion of the central nervous system (CNS) can lead to significant morbidity, including paralysis of the extremities or the diaphragm, which occurs in approximately 1 in 200 persons infected. Those with CNS manifestations of poliomyelitis are at particularly high risk of mortality, with 5% to 10% ultimately dying due to diaphragm paralysis.[1]There is no cure for polio, thus prevention is key.

An injectable polio vaccine has been available in the United States since 1955, ultimately leading to the eradication of the disease in the United States by 1979. Today the CDC recommends the polio vaccine series among the list of routine childhood vaccinations.[2]

Specific recommendations regarding vaccine administration in the United States are made by the Centers for Disease Control and Prevention (CDC) and, more specifically, the Advisory Committee on Immunization Practices (ACIP). Recommendations regarding routine childhood immunization against polio include a four-dose vaccine series of inactivated polio vaccine (IPV) given at 2 months, 4 months, 6 to 18 months, and 4 to 6 years of age. 

The third and fourth doses must be separated by at least 6 months. Due to the use of combination vaccines during childhood, some children may receive five doses of IPV, which is considered a safe practice.[3]

Alternate recommendations are provided for catch-up immunization schedules for children or accelerated vaccine series for adults or children who are traveling to areas of the world where transmission is a higher risk.

There are no routine recommendations made for adults regarding the IPV series, largely because most adults in the United States have been vaccinated as children. Those adults who are at higher risk of exposure are encouraged to consider the vaccination series. Risk of exposure may be increased by travel to endemic areas, occupational exposure, or contact with known unvaccinated persons. 

The IPV series is intended to provide protection against all known wildtype strains of the poliovirus, which includes types 1, 2, and 3.[4]

In some areas of the world, routine vaccination practice includes the oral polio virus (OPV) rather than IPV. Both series are comprised of four doses. A key difference is that the OPV is a live attenuated virus. A series begun with one formulation may be completed with the other, so long as the individual receives a total of four doses, the last dose being given as a booster between the ages of 4 and 6 years.

Though multiple formulations of polio vaccines exist, only the trivalent inactivated polio vaccine is currently used in the United States. This single-disease immunization is called poliovirus vaccine inactivated. The virus for this formulation is grown on monkey kidney tissue culture and is inactivated by formaldehyde before its incorporation into the vaccine. The vaccine does contain a preservative as well as trace amounts of polymyxin B, streptomycin, and neomycin. It is also available in its inactivated form in the combination vaccines DTaP/IPV/Hib, DTaP/Hep B/IPV, and DTaP/IPV.

Inactivated vaccines provide immunity by supplying the body’s immune system with a dose of inactivated antigen. Because this antigen is not alive, it cannot replicate in the host. Inactivated vaccines cannot cause disease, thus they may be administered to an immunocompromised host. However, their inability to replicate also confers a lesser amount of immunity, necessitating multiple doses of the vaccine. The IPV, like all other inactivated vaccines, is administered in series.

In contrast, the OPV used in other regions of the world is a live attenuated virus. The three strains of the wildtype virus are weakened in a laboratory setting prior to their incorporation into the oral vaccine. This allows the body's immune system to encounter the virus in a less threatening manner, but also to mount a humoral immune response to protect the recipient from harm with potential future exposures. 

Immunity to polio may be conferred by the use of a single antigen IPV or as part of a combination vaccine. The volume of solution injected for each is 0.5 mL, but the route of delivery differs. While single antigen IPV may be administered intramuscularly or subcutaneously, all three of the combination vaccines should be administered only intramuscularly. Site of administration depends on the patient age and size, with preference given to the anterolateral thigh in infants and the deltoid in children and adults.

In the case of the OPV, single vials contain 0.5 mL of vaccine solution, which is administered with a pipette into the mouth and swallowed by the recipient. 

Serious reactions following routine immunizations are rare. The rate of allergic reaction to routine vaccines is 1 per million doses administered. More commonly the recipient may experience a local vaccine reaction, including erythema or soreness at the injection site.

Vaccine-derived poliovirus (VDPV) presents a small risk in regions where immunization rates are low, and the oral polio vaccine (OPV) is administered. The live attenuated virus may acquire virulence, thus posing an infectious threat. It is not known to be a complication of the IPV, the only polio vaccine used in the United States for routine childhood vaccinations since 2000.

The IPV is contraindicated in individuals who have had anaphylaxis following either a previous dose of the vaccine or after taking streptomycin, polymyxin B, or neomycin, as the vaccine does contain trace amounts of these substances.

Injectable polio vaccine is both safe and recommended for administration to immunodeficient individuals and members of their household, as it is not a live vaccine. Note that the oral polio vaccine is live and should not be administered to immunocompromised persons.[5]

IPV is also safe to administer during pregnancy or to a breastfeeding mother.[6]

Adverse reactions following the receipt of the IPV are reportable to the Vaccine Adverse Event Reporting System (VAERS) per protocol.