Polio prevention

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]

Overview

Vaccination is the main form of prevention for poliomyelitis. Two types of the vaccine are available: an inactivated form (IPV), and a live-attenuated form (OPV). IPV is the current vaccine in the United States, contains all 3 serotypes of poliovirus and should be administered in 4 doses. The immune response to the vaccine produces antibodies against the 3 serotypes, which are present in 100% of the cases after the 3rd dose. The live-attenuated form may contain all serotypes of the virus or be given in the bivalent or monovalent forms. OPV immunization leads to maintenance of antibodies in circulation for up to 5 years. The monovalent form of OPV is useful to strengthen the immune response towards a specific serotype, or in cases of single serotype outbreak.

Prevention

Vaccination

As a result of the introduction of inactivated poliovirus vaccine (IPV) in the 1950s, followed by oral poliovirus vaccine (OPV) in the 1960s, poliomyelitis control has been achieved in numerous countries worldwide, including the entire Western Hemisphere. Two forms of the vaccine are available, the Inactivated Poliovirus Vaccine (IPV) and the Live-Attenuated Poliovirus Vaccine (OPV). In 1955 the Salk IPV was introduced, leading to an important reduction of endemic and epidemic poliomyelitis. However, this form of the vaccine showed low potency, since 17% of the infants who had received the vaccine, developed paralytic poliomyelitis. The OPV vaccine was introduced in 1962, as a monovalent vaccine, and the trivalent form was made available in 1964. This form of the vaccine was rapidly adopted as the main vaccine against poliomyelitis, due to:

• Better immunogenicity
• Lower cost
• Easy administration
• Vaccine virus is able to induce immunity in susceptible persons
• Induction of gastrointestinal immunity

However, because of the risk of developing Vaccine-associated paralytic poliomyelitis (VAPP) and circulating Vaccine-derived polioviruses (cVDPVs) with the OPV, countries with high polio immunization coverage (> 90%) and at low risk of wild poliovirus importation and spread including most developed countries currently only use the IPV form of the vaccine.

Inactivated Poliovirus Vaccine

Vaccine containing the inactivated and more potent forms of the virus. IPV vaccine contains all 3 serotypes of the polivirus, and may be administered concomitantly with other routine vaccines or simply as trivalent IPV. IPV should be administered in 4 doses, at the 2nd, 4th, and between the 6th and the 18th month of life, and than between the 4th and 6th year of life.

The vaccine leads to the formation antibodies against the 3 serotypes of virus, after the 2nd dose in 99% of cases, and after the 3rd dose in 100% of cases. After the 3rd dose of the vaccine, antibody titers for serotypes 1 and 3 are higher in IPV, when compared to OPV, and similar for serotype 2. Antibody titers may persist in circulation in some cases during 5 years. However the efficacy of the first two doses of IPV is thought to be inferior to the same two doses of OPV.

Children immunized with the IPV, when exposed to the live poliovirus, were more prone to shed greater amount of the virus in feces, and for a more extended period, when compared to children immunized with OPV. This indicated a greater tendency to asymptomatic poliomyelitis and to transmission of the virus in these individuals.

Oral Poliovirus Vaccine (OPV)

Live-Attenuated Poliovirus Vaccine

The live-attenuated poliovirus vaccine (OPV) is no longer available in the United States, however it is still used in other countries. The intestinal immunity induced by the virus in the vaccine is thought to be identical to the one caused by the natural virus. Commonly, after the first dose of OPV, children show the following seroconversion rates:

• Serotype 1 - 50%
• Serotype 2 - 85%
• Serotype 3 - 30%

On the second month after the third dose of OPV, the antibody prevalence to serotypes 1, 2 and 3 is > 96%. Vaccine immunization leads to maintenance of antibodies in circulation for up to 5 years. Environmental re-exposure to the vaccine virus is thought to contribute to the persistence of antibodies in the population. Following immunization with OPV, immunoglobulin A against the virus may be found in pharyngeal and duodenal secretions, between the 1st and 3rd weeks after administration, and may persist for more that 5 years.

After receiving the vaccine, nonimmune individuals shed the virus through pharyngeal secretions during 1 to 3 weeks, and through feces during 1 to 6 weeks. This shedding of the virus is considered positive, particularly in areas of poor vaccination, since it may contribute to the immunization of the community.

Monovalent

The monovalent vaccine, the Sabin oral vaccine, introduced in 1961 consisted of 3 monovalent vaccines. These were later replaced by the trivalent OPV.

In 2005, in order to enhance the global efforts for the eradication of poliovirus in certain settings, the monovalent polivirus vaccine was re-introduced. The monovalent vaccine has higher immunogenicity for a certain serotype, when compared to the polyvalent kind, due to the absence of interference with other serotypes. Additionally, the monovalent vaccine also provides a more focused approach in settings of single serotype outbreak.

Currently available OPVs

The currently available OPVs include:

(i)Trivalent OPV (tOPV) against types 1, 2 and 3
(ii)Bivalent OPV against types 1 and 3 (bOPV)
(iii)Monovalent OPV against either type 1 (mOPV1) or type 3 (mOPV3)

• WHO recommended co-ordinated withdrawal of the type 2 component of OPV due to the eradication of type 2 poliovirus since 1999. Therefore, trivalent OPV (tOPV) was replaced worldwide with bivalent OPV, this switch took place in April 2016. The monovalent OPV against type 2 will remain available only for use whenever there is type 2 poliovirus outbreak.

Safety of Oral Polio Vaccine (OPV)

OPV is safe, however very rarely serious adverse events may occur. This include:

• Vaccine-associated paralytic poliomyelitis (VAPP) and circulating vaccine-derived polioviruses (cVDPVs) may occur.
• The incidence is 2–4 cases/ million birth cohort per year in countries using OPV. Overall risk of VAPP is 1 case per 2.4 million OPV doses administered
• Outbreaks of polio due to cVDPVs occasionally occur, mainly in areas of low polio immunization coverage.

Vaccination Guidelines

The current recommended guideline for poliomyelitis immunization include:

Guidelines in Endemic and High-Risk Regions

Vaccine Type	Serotypes covered	Number of Doses	Vaccination Schedule in Endemic and High Risk Countries†
			Birth	6 weeks	10 weeks	14 weeks
OPV	*Monovalent (Either Serotypes 1 or 2 or 3) *Bivalent (Serotypes 1 & 3)‡ *Trivalent (Serotypes 1, 2, & 3)	3 to 4 doses	✔	✔	✔	✔
IPV	*Serotype 1 *Serotype 2 *Serotype 3	1 dose				✔
†Countries at high risk for importation and subsequent spread ‡Countries at high risk for importation and subsequent spread

Guidelines in Polio-eradicated Regions

Vaccine Type	Serotypes covered	Number of Doses	Vaccination Schedule in Low Risk Countries†
			2 months	4months	6 to 18 months	± Booster dose‡
IPV	*Serotype 1 *Serotype 2 *Serotype 3	3 or 4 doses	✔	✔	✔	✔
†Countries with high immunization coverage (> 90%) and at low risk of wild poliovirus importation and spread ‡4th dose (booster) is given 6months after 3rd dose of the primary series, if the 1st dose of the primary series was given before 2months of life ‡‡In the USA however, 4 doses are given at 2months, 4months, 6 to 18 months, and a booster dose at 4 to 6 years

Risk for travellers

Until the disease has been certified as eradicated globally, the risks of acquiring polio (for travellers to infected areas) and of reinfection of polio-free areas (by travellers from infected areas) remain. All travellers to and from countries and areas infected by wild poliovirus or circulating vaccine-derived polioviruses (cVDPV) should be adequately vaccinated.

Vaccine

• Both orally-administered, live attenuated polio vaccines (OPV) and inactivated poliovirus vaccines (IPV) for intramuscular (or subcutaneous) injection are widely used internationally. IPV is considered very safe. A rare adverse event associated with OPV is vaccine-associated paralytic poliomyelitis (VAPP), which occurs once in about 2.4 million doses. Outbreaks of polio due to circulating vaccine-derived polioviruses continue to be detected occasionally, mainly in areas of low immunization coverage.

• WHO no longer recommends an OPV-only vaccination schedule. For all countries currently using OPV only, at least 1 dose of IPV should be added to the schedule. In polio-endemic countries and in countries at high risk for importation and subsequent spread, WHO also recommends an OPV dose at birth (“zero dose”), followed by the primary series of three OPV doses and at least one IPV dose.
• The primary series consisting of three OPV doses plus one IPV dose can be initiated from the age of 6 weeks with a minimum interval of 4 weeks between the OPV doses. Routine vaccination with a sequential schedule using IPV followed by OPV can also be used in countries with low risk of importation of poliovirus and high vaccination coverage rate. Routine vaccination with IPV alone should be used only in countries with high vaccination coverage (>90%) and at low risk of importation and spread of wild poliovirus.
• Before travelling to areas with active poliovirus transmission, travellers from polio-free countries should ensure that they have completed the age-appropriate polio vaccination series, according to their respective national immunization schedule. Travellers to polio-infected areas who completed an OPV or IPV vaccine series >12 months previously should be given another one-time booster dose of polio vaccine. Travellers to polio-infected areas who have not received any polio vaccine previously should complete a primary schedule of polio vaccination before departure.
• Before travelling abroad, persons of all ages residing in polioinfected countries (i.e. those with active transmission of a wild or vaccine-derived poliovirus) and long-term visitors to such countries (i.e. persons who spend more than 4 weeks in the country), should have completed a full course of vaccination against polio in compliance with the national schedule. Travellers from infected areas should receive an additional dose of OPV or IPV within 4 weeks to 12 months of travel, in order to boost intestinal mucosal immunity and reduce the risk of poliovirus shedding, which could lead to reintroduction of poliovirus into a polio-free area. For persons who previously received only IPV, OPV should be the choice for the booster dose, if available and feasible. In case of unavoidable last-minute travel, travellers should still receive one dose of OPV or IPV before departure, if they have not received a documented dose of polio vaccine within the previous 12 months.
• Some polio-free countries require resident travellers and long-term visitors from polio-infected countries to provide documentation of recent vaccination against polio in order to obtain an entry visa, or they may require travellers to receive an additional dose of polio vaccine on arrival, or both.
• All travellers are advised to carry their written vaccination record (patient-retained record) in the event that evidence of polio vaccination is requested for entry into countries being visited. They should preferably use the International Certificate of Vaccination or Prophylaxis, which is available from the WHO website.

Summary of vaccine data

	Considerations for travellers for Polio vaccination
Type of vaccine	Orally administered, live attenuated polio vaccines (OPV) Inactivated poliovirus vaccines (IPV) for intramuscular (or subcutaneous) injection.
Number of doses	The primary series consists of three doses of OPV plus one of IPV. In countries at high risk for importation and subsequent spread of poliovirus, WHO also recommends an OPV dose at birth (“zero dose”). Provided that there is low risk of importation and a high immunization coverage rate, routine vaccination using IPV followed by OPV can be used. Routine vaccination with IPV alone is recommended only in countries with immunization coverage >90% and at low risk of wild poliovirus importation. WHO no longer recommends an OPV-only vaccination schedule
Contraindications	Severe allergy to vaccine components
Adverse reactions	The only serious adverse events associated with OPV are the rare occurrence of vaccine-associated paralytic poliomyelitis (VAPP) and the emergence of vaccine-derived polioviruses (cVDPV). OPV may safely be administered to pregnant women and HIV-infected persons.
Before departure	Travellers from polio-free to polio-endemic countries should have completed polio vaccination according to their national immunization schedule. Individuals who received the last dose of polio vaccine (OPV or IPV) >12 months previously should receive one booster dose. Those who are incompletely vaccinated or did not receive any polio vaccine previously should complete a primary schedule of polio vaccination before departure. Persons residing in countries with active transmission of a wild or vaccine-derived poliovirus or long-term visitors to such countries should have completed a full course of vaccination against polio according to national recommendations. Travellers from infected areas should receive an additional dose of OPV or IPV at least 4 weeks before departure. Urgent travellers who did not receive any polio vaccine within the previous 12 months should still be given one dose of OPV or IPV before departure
Special precautions	To obtain an entry visa some polio-free countries require a certificate of recent polio vaccination from travellers coming from polio-affected countries. In some cases, an additional dose of polio vaccine is provided on arrival.