Poliomyelitis (Polio)

Polio is a highly infectious viral disease that mainly affects young children. It can invade the nervous system and cause irreversible paralysis. There is no cure for polio; it can only be prevented by immunization. The polio vaccine, given multiple times, can protect a child for life. Maintaining high population immunity is essential to interrupt transmission, prevent outbreaks and protect progress towards a polio-free world.

Of the three strains of wild poliovirus (type 1, type 2 and type 3), wild poliovirus type 2 and 3 have been eradicated.  The Global Polio Eradication Initiative (GPEI) is working to interrupt wild poliovirus type 1 (WPV1) transmission and stop outbreaks caused by circulating vaccine-derived polioviruses (cVDPVs), also referred to as circulating variant polioviruses.

Different vaccines are used for routine immunization and outbreak response. Vaccine choice depends on the poliovirus type, population immunity, the national schedule and the epidemiological situation.

IPV and IPV-containing vaccines

Inactivated poliovirus vaccine (IPV) protects against poliovirus types 1, 2 and 3 and cannot cause vaccine-associated paralytic poliomyelitis. IPV may be given as a standalone vaccine, as fractional-dose IPV (fIPV) where recommended, or as part of an IPV-containing combination vaccine such as a hexavalent vaccine. OPV-using countries should include at least two IPV doses, and countries that have not introduced IPV2 should do so urgently. A completed three-dose IPV-containing primary series beginning at 6 weeks of age or later does not require an additional scheduled IPV booster.

Bivalent oral polio vaccine

Bivalent oral polio vaccine (bOPV) protects against types 1 and 3 and induces intestinal immunity that helps interrupt transmission. In countries giving three IPV doses in the first year of life, routine bOPV may be reduced from three doses to two where the risk of poliovirus importation and spread is low. Other countries should follow current WHO risk-based recommendations and their national schedule. The eventual cessation of bOPV will be globally coordinated.

Novel oral polio vaccine type 2

Novel oral polio vaccine type 2 (nOPV2) is the preferred vaccine for cVDPV2 outbreak response. It is designed to be more genetically stable than Sabin monovalent OPV type 2, reducing the risk of new variant poliovirus emergences while retaining the ability to interrupt type 2 transmission.

Hexavalent vaccines

Hexavalent vaccines are IPV-containing combination vaccines that provide protection against poliomyelitis and against diphtheria, tetanus, pertussis, hepatitis B and Haemophilus influenzae type b (Hib). Whole-cell (DTwP-HepB-Hib-IPV) and acellular (DTaP-HepB-Hib-IPV) formulations are available. For countries introducing whole-cell hexavalent vaccine, a three-dose primary series can provide three IPV-containing doses and simplify delivery by replacing separately administered pentavalent vaccine and IPV. Hexavalent vaccines do not contain OPV, so countries using bOPV should continue it according to current WHO recommendations and the national schedule.

High routine immunization coverage and timely catch-up vaccination are essential to close immunity gaps, particularly among zero-dose and under-immunized children. Fixed, outreach and mobile services, community engagement and local data should be used to reach high-risk and underserved populations, including in fragile, conflict-affected and humanitarian settings.

Acute flaccid paralysis surveillance, wastewater and environmental surveillance, laboratory and genomic surveillance, and surveillance in selected settings for prolonged poliovirus excretion among people with primary immunodeficiency disorders provide complementary approaches to detecting poliovirus and guiding response. High-quality surveillance must continue after transmission is interrupted.

Any detection of wild or variant poliovirus requires rapid investigation, risk assessment and a high-quality response in accordance with current GPEI outbreak-response standard operating procedures.

Achieving and sustaining a polio-free world requires interrupting and certifying WPV1 eradication, eliminating cVDPV2, eventually coordinating a global cessation of OPV, maintaining protection with IPV, strengthening surveillance, ensuring rapid outbreak preparedness and response, securing vaccine stockpiles, and containing poliovirus materials. IPV-containing combination vaccines, including hexavalent vaccines, provide an important option for sustaining IPV delivery through routine immunization.