Poliomyelitis

Introduction

Infectious agent

Polioviruses (genus Enterovirus) are small, non-enveloped viruses with a single-stranded RNA genome. Polioviruses are rapidly inactivated by chlorine, formaldehyde, heat, and ultraviolet light. Poliovirus has 3 serotypes, 1, 2, and 3, that evoke minimal heterotypic immunity between them.

Transmission

Transmission occurs when the virus enters through the mouth and multiplies in the throat and gastrointestinal tract. Virus can be excreted in nasopharyngeal secretions for 1–2 weeks and in stool for 3–6 weeks, even in people who develop no symptoms after infection. Transmission occurs from person to person through the oral and fecal-oral routes.

Epidemiology

Before a vaccine was available, infection with wild poliovirus (WPV) was common worldwide and had seasonal peaks and epidemics in the summer and fall in temperate areas. The incidence of poliomyelitis (polio) in the United States declined rapidly after the licensure of inactivated poliovirus vaccine (IPV) in 1955 and live oral poliovirus vaccine (OPV) in the 1960s. The last cases of indigenously acquired polio caused by WPV in the United States occurred in 1979, and the last imported polio case caused by WPV was reported in 1993. However, in 2022 a polio case caused by circulating vaccine-derived poliovirus type 2 (cVDPV2) and associated silent community transmission were identified in New York State.

Built on the success achieved in the Americas, the Global Polio Eradication Initiative (GPEI) began in 1988 and has made great progress in interrupting WPV transmission globally. Type 2 WPV was last isolated in 1999 and was declared eradicated in 2015; type 3 WPV was last detected in November 2012 and was declared eradicated in 2019. In 2021, type 1 WPV endemic circulation persisted in only 2 countries, Afghanistan and Pakistan. Despite achievements in eradicating WPV globally, polio-free countries with low vaccination coverage remain at risk for poliomyelitis outbreaks after importation of WPV. In February 2022, a person in Malawi (onset of paralysis, November 2021) was identified with type 1 WPV 18 months after Africa was certified free of indigenous WPV (in August 2020). The virus isolated from this patient was genetically linked to a type 1 WPV lineage last detected in Pakistan in 2019. WPV spread into Mozambique, causing 8 additional poliomyelitis cases in 2022.

Countries that have low OPV coverage in routine immunization also are at risk of poliomyelitis outbreaks caused by circulating vaccine-derived poliovirus (cVDPV). The live attenuated poliovirus strains contained in the Sabin or novel OPV can circulate in areas with inadequate OPV coverage and revert to having wild-like characteristics. Rarely, OPV can cause paralytic poliomyelitis in vaccine recipients or their close contacts, known as vaccine-associated paralytic poliomyelitis.

Because >90% of cVDPV cases detected between 2006 and 2014 were serotype 2, and WPV2 had long been eradicated, all OPV-using countries conducted a synchronized switch from trivalent OPV (tOPV, containing serotypes 1, 2, and 3) to bivalent OPV (bOPV, containing serotypes 1 and 3) in April 2016. Unfortunately, undetected transmission of type 2 cVDPV before the tOPV switch, together with delayed and suboptimal vaccination campaigns with type 2 OPV during 2018–2019, resulted in spread of type 2 cVDPV from initial reservoirs and generation of new outbreaks throughout Africa and Asia, that also reached Europe and the Americas. Type 2 cVDPV outbreaks caused 1,082 polio cases in 24 countries in 2020, 685 cases in 22 countries in 2021, and 689 cases in 20 countries in 2022, including one case in the United States. During 2020–2022, type 1 cVDPV caused 245 polio cases in 7 countries and WPV caused 176 polio cases in 4 countries. During 2023, 395 type 2 cVDPV cases in 23 countries, 134 type 1 cVDPV cases in 3 countries, and 12 WPV cases in 2 countries were reported.

Travelers to countries with current or recent WPV or cVDPV outbreaks can be at risk for exposure to poliovirus. The last documented case of WPV-associated paralysis in a U.S. resident traveling abroad occurred in 1986 in a 29-year-old vaccinated adult who had been traveling in South and Southeast Asia. In 2005, an unvaccinated U.S. adult traveling abroad acquired vaccine-associated paralytic poliomyelitis after contact with an infant recently vaccinated with OPV. Of special concern are people with underlying primary immunodeficiencies that prevent an adequate antibody response to viruses; they are at a greater risk for prolonged poliovirus infection and paralysis from WPV or cVDPV or after exposure to people recently vaccinated with OPV.

For additional information on the status of polio eradication efforts, countries or areas with active WPV or VDPV circulation, and vaccine recommendations, consult the GPEI website and the polio travel health notices on the Centers for Disease Control and Prevention's (CDC's) Travelers' Health website.

Clinical presentation

Most poliovirus infections are asymptomatic; approximately 25% cause minor short-term illness. Depending on poliovirus serotype, approximately 1 in 200 to 1 in 2,000 infections are associated with paralysis. Paralysis affects ≥1 limbs, and in severe cases can result in quadriplegia, respiratory failure, and rarely, death. Adults who develop paralysis usually have more severe disease and a worse prognosis than children. Residual paralysis occurs in about two-thirds of cases. For many people with residual deficits, and even for some who recover fully, worsening of weakness or paralysis can occur 20–30 years later, known as post-polio syndrome.

Diagnosis

Information on diagnostic testing for poliovirus is available from CDC's Polio Laboratory Testing website and Test Directory: Submitting Specimens to CDC.

Poliovirus can be detected in clinical specimens (usually stool) obtained from an acutely ill patient. Shedding in fecal specimens can be intermittent and declines over time, but poliovirus can be detected for up to 60 days after onset of paralysis. During the first 3–10 days after paralysis onset, poliovirus also can be detected from oropharyngeal specimens, but stool specimens are the preferred source for diagnosis. Poliovirus rarely can be detected in the blood or cerebrospinal fluid. In most cases, blood antibody titers are not useful for diagnosis.

Poliovirus is detected by virus isolation in cultured cells. PCR testing of poliovirus isolates can identify the serotype and whether it is WPV, VDPV, or a vaccine (Sabin or novel) strain. Genomic sequencing of poliovirus isolates can determine the geographic origin of WPV, confirm VDPV presence, estimate the time of VDPV circulation since the original OPV dose, and establish genetic linkages among VDPVs isolated from human or environmental sources to track outbreaks.

Paralytic polio is designated an immediately notifiable, urgent disease, which requires state and local health authorities to notify CDC within 24 hours of identification. There are safety requirements for handling polioviruses; specimens from suspected paralytic polio cases in the United States should be shipped to the CDC laboratory for testing. Notify CDC through the Emergency Operations Center (EOC, 770-488-7100) or through state health authorities. CDC's EOC will connect callers with polio subject matter experts who can provide consultation regarding the collection of clinical specimens and procedures.

Treatment

No licensed treatment exists for poliovirus infection, and only supportive care for symptoms is available. Two antiviral agents are undergoing clinical testing for the treatment of people with immunodeficiencies who are infected with and excreting immunodeficiency-associated VDPV.

Prevention

Vaccine

Health protection recommendations

Since 2000, IPV is the only polio vaccine available in the United States, but bivalent OPV is used in most low- and middle-income countries for routine immunization series and for global polio-eradication activities. In response to type 2 cVDPV outbreaks, the population should be immunized with genetically stabilized novel OPV2. Monovalent OPV2 is no longer used in responses; trivalent OPV was used when serotype co-circulation occurred, as in Afghanistan and Pakistan. For countries that do not use bivalent OPV in routine immunization and have high sanitation standards, a timely initial response may be conducted with IPV only, but widespread transmission in the general population warrants an OPV response according to the World Health Organization (WHO). For complete information on recommendations for poliomyelitis vaccination, consult the Advisory Committee on Immunization Practices website and the June 2022 WHO position paper on poliovirus vaccines.

Before travelers go to areas where WPV or VDPV is circulating, ensure that they have completed the recommended age-appropriate polio vaccine series (see Infants and Children, later in this chapter). Adults traveling to those areas who have completed a primary series may receive a single lifetime IPV booster dose. Based on historical evidence of cross-border transmission, travelers going to countries that border areas with WPV or VDPV circulation and who also have a high risk for exposure to someone with imported infection (e.g., will be working in healthcare settings, refugee camps, or other humanitarian aid settings) may also receive a single lifetime IPV booster.

Countries are considered to have WPV or cVDPV circulation if they have evidence of poliovirus transmission during the previous 12 months (endemic circulation of WPV, active WPV or cVDPV outbreaks, or environmental isolation through sewage sampling). Because poliovirus circulation and outbreak responses are dynamic, refer to CDC's Travelers' Health website destination pages for the most up-to-date polio vaccine recommendations by country.

Country requirements

In May 2014, the director-general of WHO declared the international spread of poliovirus to be a public health emergency of international concern under the authority of the International Health Regulations (IHR). To prevent further spread of virus, WHO issued temporary polio vaccine recommendations for travelers staying >4 weeks and residents departing from countries with risk for poliovirus spread. The IHR emergency committee on polio meets every 3 months and updates the list of countries that should continue the temporary polio vaccine recommendations to reduce the risk for international spread of poliovirus. See updated IHR reports at Poliovirus IHR Emergency Committee.

If implemented by a country, the polio vaccine must be received 4 weeks to 12 months before the date of departure from the polio-affected country. Be aware that long-term travelers and residents might be required to show proof of polio vaccination when departing from these countries and to document all polio vaccination administration on an International Certificate of Vaccination or Prophylaxis (ICVP). Country requirements might change, so check for updates on the CDC Travelers' Health website for a list of affected countries and guidance on meeting the vaccination requirements. Use the link for ordering information and instructions on how to fill out the ICVP.

Adults

Before traveling to areas where WPV or VDPV is circulating, adults who are unvaccinated or incompletely vaccinated should receive a series of 3 doses: 2 doses of IPV administered 4–8 weeks apart, and a third dose administered 6–12 months after the second dose. If 3 doses of IPV cannot be administered within the recommended intervals, alternative dosing schedules are available (Table 4.14.1).

Table 4.14.1: Alternative adult polio vaccine dosing schedules

Immunocompromised people

IPV can be safely administered to immunocompromised travelers and their household contacts (see Immunocompromised Travelers chapter). Although a protective immune response cannot be ensured, IPV might confer some protection to people who are immunocompromised. Those with certain primary immunodeficiency diseases should not be given OPV and should avoid contact with children vaccinated with OPV overseas in the previous 6 weeks.

Infants and children

In the United States, all infants and children should receive 4 doses of IPV, given at ages 2, 4, and 6–18 months, and 4–6 years. This is generally administered as a component of combination vaccines. The final dose should be administered at ≥4 years of age, regardless of the number of previous doses, and should be given ≥6 months after the previous dose. A fourth dose in the routine IPV series is not necessary if the third dose was administered at ≥4 years of age and ≥6 months after the previous dose. If the routine series cannot be administered within the recommended intervals before protection is needed, CDC recommends the following alternative: give the first dose to infants at ≥6 weeks of age, give the second ≥4 weeks after dose 1, and the third dose ≥4 weeks after dose 2, then give the fourth dose ≥6 months after dose 3.

If the age-appropriate series is not completed before international travel, administer the remaining IPV doses to complete a full series when feasible, at the intervals recommended above. In addition, children completing the accelerated schedule should still receive a dose of IPV at ≥4 years of age, provided ≥6 months have passed since the last dose.

Children who received poliovirus vaccine outside the United States

Vaccines administered outside the United States generally can be accepted as valid doses if the schedule is similar to that recommended in the United States. Vaccination against polio is also valid for children from countries that use an accelerated schedule. Only written, dated records are accepted as evidence of previous vaccination. Please see Guidance for Assessment of Poliovirus Vaccination Status and Vaccination of Children Who Have Received Poliovirus Vaccine Outside the United States and its erratum for information on interpreting international poliovirus vaccination documentation.

Children with full vaccination status who received only bOPV in the primary series because they were born after April 2016, or who received a combination of tOPV and bOPV, should be revaccinated with a full IPV series to ensure protection against all 3 poliovirus types. If the child has documentation of receipt of 1 or 2 IPV doses, these doses can be considered as part of the U.S. dosing schedule to be completed with 2–3 additional IPV doses. In accordance with the age-appropriate U.S. IPV schedule, vaccinate or revaccinate children <18 years old without adequate documentation of poliovirus vaccination.

International adoption from countries or areas where WPV or VDPV is actively circulating is a special situation. International adoptees might not have completed a primary polio vaccination series nor received a polio vaccine dose before departure. Thus, although the risk is small, they could be infected with WPV or VDPV and remain infectious upon entry into the United States and potentially transmit to U.S. household members and caregivers. As a measure of prudence, the polio vaccination status of all household members and caregivers of international adoptees from a country with active WPV or VDPV circulation should be assessed before the child enters the United States. People who are unvaccinated, incompletely vaccinated, or whose vaccination status is unknown should be brought up to date.

Pregnancy and breastfeeding

If a pregnant woman is unvaccinated or incompletely vaccinated and requires immediate protection against polio because of planned travel to a country or area where WPV or VDPV is actively circulating, IPV can be administered as recommended for adults (see Pregnant Travelers chapter). Breastfeeding is not a contraindication to receiving polio vaccine (see Travel and Breastfeeding chapter).

Precautions and contraindications

IPV can be administered to people with diarrhea. Minor upper respiratory illnesses with or without fever, mild to moderate local reactions to a previous dose of IPV, current antimicrobial therapy, and the convalescent phase of acute illness are not contraindications to vaccination. IPV can be co-administered with other vaccines.

Safety and adverse reactions

Minor local reactions (pain and redness) can occur after IPV administration. Do not administer IPV to people who have experienced a severe allergic reaction (e.g., anaphylaxis) after a previous dose of the vaccine. Because IPV contains trace amounts of neomycin, polymyxin B, or streptomycin, hypersensitivity reactions can occur after IPV administration among people allergic to these antibiotics.