Polio Vaccine

Mechanism of Action

IPVs contain inactivated (killed) forms of all 3 poliovirus types. Available vaccines include the Salk IPV, which contains WPV strains, and the Sabin IPV, which contains Sabin strains. The Sabin IPV has limited global use and is unavailable in the United States. The modern Salk IPV is more antigenic than earlier versions, often referred to as enhanced IPV.[World Health Organization. Polio vaccines: WHO position paper – June 2022]

Polioviruses for IPV are grown in human diploid cells or Vero cell culture and inactivated with formaldehyde before being incorporated into the vaccine. The inactivated antigens produce a robust humoral response in the vaccine recipient but limited mucosal immunity. Compared to individuals experiencing primary infection, those vaccinated with IPV shed less poliovirus from the pharynx but similar amounts through the gastrointestinal tract.[9][World Health Organization. Polio vaccines: WHO position paper – June 2022] Thus, polioviruses can spread undetected for months, even in polio-free countries with high overall IPV vaccination rates. Poverty, crowding, inadequate water, poor sanitation, and other associated socioeconomic factors increase the likelihood of spread. When administered after exposure to WPV or OPV, IPV also boosts mucosal immunity.[World Health Organization. Polio vaccines: WHO position paper – June 2022] Because IPV contains an inactivated virus, it cannot replicate in the host or cause disease.

OPVs contain live viruses intentionally weakened through repeated passage in non-human cell cultures to reduce their virulence and transmissibility.[World Health Organization. Polio vaccines: WHO position paper – June 2022] Following inoculation, the viruses in the vaccine replicate in the oropharynx and intestine, similarly to WPV.[CDC. Chapter 18: Poliomyelitis] Immunocompetent patients develop mucosal and humoral immune responses to the poliovirus following OPV vaccination. Following immunization, most non-immune individuals who receive OPV shed vaccine-derived poliovirus from the pharynx for a few days and from the stool for 4 to 6 weeks. Contact with viruses shed by OPV vaccination individuals enhances immunity among household members and others close to these individuals, thereby extending the impact of vaccination programs.[World Health Organization. Polio vaccines: WHO position paper – June 2022] 

Host mucosal immunity suppresses the replication and excretion of poliovirus, reducing the risk of transmission during subsequent exposure to wild-type or vaccine-derived polioviruses.[World Health Organization. Polio vaccines: WHO position paper – June 2022] However, individuals with B-cell immunodeficiency lack sufficient mucosal immunity, increasing their risk of developing paralytic disease and experiencing prolonged shedding of OPV.

Affordable, easy to administer, and effective in halting transmission, OPVs remain vital tools for global polio eradication, primarily used in endemic countries and at risk of reintroduction of WPV. Although immensely successful in eliminating the WPV, the high mutability of the virus causes vaccine-associated paralytic polio and has led to the emergence of circulating vaccine-derived polioviruses. Novel OPVs have enhanced genetic stability compared to the original OPVs, created by modifying the genomes of the original Sabin OPV strains at specific locations—domain V, cre-element, and RNA-dependent RNA polymerase.[World Health Organization. Polio vaccines: WHO position paper – June 2022]

Please refer to the Adverse Effects section for more information on vaccine-derived polioviruses.

Administration

GPEI. The Vaccines.GEI. The Vaccines.Inactivated Polio Vaccine

In children and infants, IPV is preferentially administered as part of multivalent vaccines for multiple routine childhood diseases, such as pentavalent or hexavalent vaccines with diphtheria-tetanus-acellular pertussis, Haemophilus influenza type b, hepatitis B, or, most recently, whole-cell pertussis.[9][World Health Organization. Polio vaccines: WHO position paper – June 2022] Ideally, clinicians should provide IPV with a tetanus or pertussis booster in adults. No interference occurs with the coadministration of IPV with other vaccines. The site of IPV administration depends on the patient's age and size, with preference given to the anterolateral thigh in infants and the deltoid in children and adults.

Standalone IPV is a 0.5 mL intramuscular injection used most frequently for patients with sufficient immunity to other diseases or require rapid development of immunity. For example, clinicians may provide standalone IPV to travelers heading to an endemic area or individuals presenting to vaccination clinics during campaigns or outbreak responses in endemic countries. Some countries use standalone IPV administered as a subcutaneous fractional dose (0.1 mL or one-fifth of a regular dose) in vaccination campaigns to extend vaccine supply and decrease costs. IPV may be administered safely to immunocompromised, pregnant, and breastfeeding individuals.[World Health Organization. Polio vaccines: WHO position paper – June 2022] Although the CDC advises precautions regarding IPV use in pregnancy—as with other inactivated vaccines—patients at increased risk of exposure may still receive the vaccine.[CDC. Chapter 18: Poliomyelitis]

IPV remains stable at 3 to 8 °C for 3 years and should not be frozen. Multidose vials containing 5 or 10 doses can be used for up to 28 days after opening.[World Health Organization. Polio vaccines: WHO position paper – June 2022] The vaccine may contain trace amounts of formaldehyde, polymyxin B, streptomycin, or neomycin.[10][11][World Health Organization. Polio vaccines: WHO position paper – June 2022] IPV does not contain thiomersal, as this decreases its immunogenicity. Multidose vials of IPV contain 2-phenoxyethanol as a preservative.

Oral Polio Vaccine

One dose of OPV (0.1 mL) is administered directly into the mouth using a dropper or dispenser. Vaccinators can coadminister OPV with other routine childhood antigens such as diphtheria-tetanus-acellular pertussis, pneumococcal conjugate, hepatitis B, measles, and Haemophilus influenza type b. Interference with other vaccines or increases in adverse effects does not occur with the coadministration of these antigens.[World Health Organization. Polio vaccines: WHO position paper – June 2022] Current evidence does not suggest whether OPV interferes with the rotavirus and Bacillus Calmette-Guérin (BCG) vaccines.

OPV is available only in multidose vials and requires freezing for long-term storage. After defrosting, the vaccine remains stable for 6 months at 2 to 8 °C.[World Health Organization. Polio vaccines: WHO position paper – June 2022] As the virus is highly heat sensitive, OPV vials have monitors to indicate exposure to heat. Heat-exposed vials should not be used for immunization. The vaccine may contain trace amounts of antibiotics.

Effectiveness

Seroconversion rates following the administration of IPV and OPV vary across settings, polio types, age of vaccine receipt, and interval between doses. Despite these variations, the effectiveness of the vaccines in preventing paralytic polio is high. A completed IPV series alone protects more than 99% against severe disease.[4][CDC. Polio Vaccination]

In high-income countries, OPV has a similar effectiveness to IPV at greater than 95%.[9][10][World Health Organization. Polio vaccines: WHO position paper – June 2022] Studies conducted in low-income settings show a more variable and less robust humoral immune response, with an average seroconversion rate of 73%.[9][World Health Organization. Polio vaccines: WHO position paper – June 2022] This discrepancy is likely due to various factors, including maternal antibodies, host intestinal immunity, nutritional status, household exposure to OPV, enteric infections, and geographic location. The effectiveness of a new, more genetically stable OPV2 is non-inferior to that of monovalent OPV2, with no safety concerns found after administering the first 65 million doses.[10][GPEI The Vaccines] A birth dose of bivalent OPV provides infants with limited immunity in the near term but increases antibody levels after subsequent routine childhood immunization.[World Health Organization. Polio vaccines: WHO position paper – June 2022]

Adverse Effects

Inactivated Polio Vaccine

The safety profile of IPV is excellent whether administered alone or as part of a combination vaccine. Recipients may experience a minor local reaction within 48 hours of vaccination, which may include erythema (0.5% to 1.5%), induration (3% to 11%), or pain (14% to 29%) at the injection site.[World Health Organization. Polio vaccines: WHO position paper – June 2022] Up to 38% of recipients may develop a fever of 39 °C or higher.[CDC. Chapter 18: Poliomyelitis] Uncommon minor adverse reactions include irritability, fatigue, anorexia, and nausea. The frequency and severity of reactions following diphtheria-tetanus-pertussis alone are similar.

IPV may rarely cause hypersensitivity or anaphylactic reactions to vaccine components.[CDC. Chapter 18: Poliomyelitis] Allergic reactions occur in 1 in every million doses. There is no risk of vaccine-associated paralytic polio with IPV use.

As with other vaccines, serious adverse effects following the receipt of the inactivated polio vaccine in the United States should be reported to the Vaccine Adverse Event Reporting System (VAERS).

Oral Polio Vaccine

Like IPV, the OPV is generally very well-tolerated. However, the vaccine causes 2 rare but severe events—vaccine-associated paralytic polio and circulating vaccine-derived paralytic polio, clinically indistinguishable from paralytic polio due to WPV.

Vaccine-associated paralytic polio results from the proliferation and mutation of polioviruses in OPV recipients or their contacts. Replicating viruses in the intestine revert to neurovirulent variants demonstrating close genetic similarity to the vaccine strain. Vaccine-associated paralytic polio occurs an estimated 0.42 times per million doses of OPV,[9][CDC. Chapter 12: Poliomyelitis] or 3.8 times (range 2.9 to 4.7) per million births in countries that use trivalent OPV.[1][11] [World Health Organization. Polio vaccines: WHO position paper – June 2022] In high-income countries, vaccine-associated paralytic polio occurs most commonly after the first dose of OPV and in immunocompromised individuals, in whom the risk of vaccine-associated paralytic polio is approximately 3000 times higher compared to those without immunocompromise.[1] In low-income countries, vaccine-associated paralytic polio primarily affects children aged 1 to 4 receiving second or subsequent doses.[11][World Health Organization. Polio vaccines: WHO position paper – June 2022] Due to viral excretion in the stool, ongoing transmission can occur. Many national public health authorities replace OPV with IPV following regional poliovirus elimination to eliminate the risk of vaccine-associated paralytic polio while maintaining high population immunity.

Vaccine-derived poliovirus results from the naturally selective proliferation of OPV viruses in populations with low herd immunity, leading to circulating vaccine-derived polioviruses, or from prolonged carriage in immunocompromised individuals, resulting in immunodeficiency-associated vaccine-derived polioviruses. Recombination with other enteroviruses or reversion of OPVs allows the resulting circulating vaccine-derived polioviruses to regain the neurovirulence and transmissibility of WPV.[1][World Health Organization. Polio vaccines: WHO position paper – June 2022] Genetic divergence of circulating vaccine-derived polioviruses from the attenuated OPV virus indicates prolonged replication and circulation.

The first detection of circulating vaccine-derived poliovirus occurred during a polio outbreak on the island of Hispaniola in 2000. Currently, circulating vaccine-derived polioviruses are responsible for the majority of poliomyelitis cases. Most cases of paralysis associated with circulating vaccine-derived polioviruses take place in sub-Saharan Africa and Asia, with a total of 345 cases reported between July 2023 and July 2024.[World Health Organization. Polio eradication strategy 2022–2026: delivering on a promise] This number compares to 881 cases in 2022 and 524 in 2023. Although the total cases in 2023 decreased from 2022, the geographical spread of circulating vaccine-derived poliovirus was broader in 2023.[12]

The WHO estimated that OPV2 was responsible for approximately 40% of vaccine-associated paralytic polio cases and 90% of circulating vaccine-derived poliovirus before the removal of OPV2 from vaccinations in 2016. Considering the millions of doses administered annually, even the low rates of paralytic polio present a significant concern for OPV's continued use and the eradication of the poliovirus.[1]

Vaccine-associated paralytic polio and circulating vaccine-derived poliovirus cases are reportable under the VAERS.

Contraindications

Inactivated Polio Vaccine 

IPV is contraindicated in individuals with hypersensitivity to the vaccine or any of its components, including 2-phenoxyethanol and formaldehyde, or after taking antibiotics that may be present in the vaccine in trace amounts.

Minor diarrheal or upper respiratory illness with or without fever, minor or moderate local reactions to a previous dose of vaccine, and current antibiotic therapy are not contraindications for vaccine receipt. IPV is safe and recommended for administration to immunodeficient individuals and household members, as it is not a live vaccine.

The WHO considers IPV to be safe for administration during pregnancy or breastfeeding.[13][14] The CDC, however, considers pregnancy a precaution for IPV administration.[CDC. Chapter 12: Poliomyelitis]

Oral Polio Vaccine

OPVs are contraindicated in individuals with a history of allergy to the vaccine or to trace antibiotics it may contain. The OPV is live and should not be administered to patients with severe immunodeficiency, including those with primary immunodeficiency disorders, those receiving radiation therapy that targets immune cells, or those on chemotherapeutic or other drugs that have immunomodulatory properties, such as high-dose systemic corticosteroids, alkylators, and Tumor necrosis factor-alpha inhibitors.[15] IPV is preferably given before initiating immunocompromising therapy.[6]

The WHO considers it safe to administer OPV in pregnant women and asymptomatic HIV-positive individuals. Asymptomatic HIV infection does not decrease the immune response, lead to prolonged shedding, or increase the risk for vaccine-associated paralytic polio in vaccine recipients.[World Health Organization. Polio vaccines: WHO position paper – June 2022]

Asymptomatic HIV infection does not reduce immune response, prolong shedding, or increase the risk of vaccine-associated paralytic polio in vaccine recipients.

Monitoring

Polio vaccination does not require any monitoring for immunity right after vaccination or in the long term. Although evidence of seroconversion after polio vaccination correlates highly with effectiveness, antibody levels can wane over the decades, and titers may dip below detectable levels. No evidence suggests the loss of detectable antibodies results in a loss of protection after initial seroconversion.[World Health Organization. Polio vaccines: WHO position paper – June 2022]

Protection against paralytic disease lasts for decades after completing a primary vaccine series with either vaccine and may be lifelong.[10][World Health Organization. Polio vaccines: WHO position paper – June 2022] The recommendation for a single adult booster in individuals at increased risk is based on uncertainty in the duration of immunity and evidence of high and consistent immunity boosting with a single adult dose.

Enhancing Healthcare Team Outcomes

The interprofessional healthcare team is pivotal in planning, monitoring, and administering polio vaccinations. Counseling people who are vaccine-hesitant, providing routine vaccines in the primary care office, pharmacy, or public health clinic, delivering mass immunization campaigns to control outbreaks, and monitoring vaccination rates are examples of interprofessional team functions contributing to polio eradication.

Outbreak Control

Coordinated immunization activity between public health authorities, clinicians, pharmacists, community agencies, community health workers, and other healthcare providers is critical for rapid polio outbreak control. An outbreak is defined as 2 or more genetically linked polioviruses from patients, asymptomatic contacts or carriers, or environmental samples.[16] The WHO and national and local governments provide essential support for vaccine program implementation during outbreaks.

Using the polio vaccine appropriate to the poliovirus outbreak strain rapidly interrupts transmission and stops outbreaks due to wild-type or circulating vaccine-derived poliovirus. Based on local epidemiology and the circumstances of the outbreak, public health authorities may recommend IPV or monovalent, bivalent, or trivalent OPVs. Novel OPV2 was licensed under Emergency Use Listing in 2020 for response to outbreaks of circulating vaccine-derived poliovirus type 2.[World Health Organization. Polio vaccines: WHO position paper – June 2022] The vaccine remains in limited supply, necessitating the continued use of OPV2 in some outbreak situations. Novel OPV2 is not used in routine immunization programs.

Improving Vaccine Coverage Rates

The interprofessional healthcare team has a crucial role in improving polio vaccination rates, which are suboptimal in many jurisdictions. Globally, the coverage rate for 3 doses of either OPV or IPV at 12 months was approximately 84% in 2022.[12] This rate compares to an estimated coverage rate of 81% and 83% in 2021 and 2022 and an 85% to 87% average between 2014 and 2019, reflecting the impact of the COVID-19 pandemic on polio and other routine vaccinations.

The global vaccination rates for at least 1 dose of IPV after bivalent OPV were 83% in 2019, 80% in 2020 and 2021, and 84% in 2022.[12] The estimated coverage rates of 3 OPV doses and at least 1 IPV dose were 76% and 71% in Afghanistan and 85% and 90% in Pakistan in 2022. However, rates in areas with circulating WPV1 are much lower.[17][12]

Among children younger than 2 in the United States born in 2017-2018 and 2019-2020, vaccination rates were 92.6% and 93.0% for at least 3 doses of IPV.[18] These rates indicate the United States maintained vaccination rates in this age group in the early stages of the COVID pandemic. However, rates are variable across populations. Specifically, infants who are non-Hispanic White, living at or above the poverty line, privately insured, or living in urban areas have higher vaccination rates. The differences can be stark. For example, 95.6% of infants with full private insurance had 3 or more doses of IPV, compared to 80.0% of those without insurance.[18] A lower rate of attachment to the healthcare system is a critical barrier in this group.[17] Other children eligible for the Vaccines for Children program likewise had lower polio vaccination rates than entirely privately insured children, with lower completion rates of multi-dose vaccines following the first year of life.

An increasing number of parents are reluctant to provide polio or other vaccinations for their children, a preexisting problem that worsened during the pandemic. Through building relationships, consistent messaging, and answering all questions, the interprofessional team can gain the trust of patients and their families and improve vaccination rates. The inactivated polio vaccine has no long-term adverse effects. Furthermore, the complications of acquiring polio can be severe and long-lasting. OPV is the primary contributor towards a greater than 99.9% reduction in polio around the world, and severe side effects are extremely rare.GPEI. The Vaccines

Many unvaccinated or under-vaccinated people in the United States and elsewhere have inadequate opportunities for immunization due to time; logistics; costs associated with financial barriers, such as copayments, childcare, and transportation; bureaucratic hurdles; or a multitude of other factors.[19][17] A lack of awareness about available services or the absence of nearby, patient-centered healthcare options further contributes to lower vaccination rates. For example, services requiring multiple visits or visits across different providers can cause barriers, and patients may be unaware of the United States Vaccines for Children Program. Coordinated activity across interprofessional teams and others reduces barriers and increases opportunities for vaccination.

Using open communication and data sharing, the interprofessional healthcare team can leverage non-governmental agencies, community leaders, governments, and others to educate the public about the risks and benefits of polio and other vaccinations, overcome vaccine hesitancy, and contribute to patient and public health.

Supplementary immunization activities, also known as vaccination campaigns, are an important way to increase local vaccination rates in areas not adequately covered by routine immunization programs and to control outbreaks. The WHO recommends bivalent or monovalent OPV for these activities, depending on the epidemiology and purpose of the campaign.[World Health Organization. Polio eradication strategy 2022–2026: delivering on a promise] In 2023, 30 countries carried out 119 vaccine campaigns.[12]

The Evolution of Polio Immunization

Since Jonas Salk developed the first polio vaccine in 1955, public health authorities, clinicians, researchers, and healthcare providers have improved and adapted polio immunization technologies and strategies to address current challenges optimally. Sabin OPV largely replaced Salk IPV in the 1960s due to OPV's lower cost, ease of administration, and ability to prevent onward transmission. Trivalent OPV—OPV1, OPV2, and OPV3—replaced the original monovalent OPVs—OPV1, OPV2, or OPV3—starting in 1963. Polio-free countries switched to enhanced IPVs, as the risks of vaccine-associated paralytic polio and circulating vaccine-derived polioviruses outweighed the benefits of OPV. In 2016, the GPEI organized a coordinated global switch from trivalent to bivalent OPV (OPV1 and OPV3) due to increasing global rates and expanding distribution of circulating vaccine-derived poliovirus type 2. In 2022, the WHO recommended adding 2 doses of IPV in countries that previously used only OPV. The recent availability of novel OPV2 for outbreak control is one of the latest updates to the strategy over time.

New approaches remain essential. The vaccination strategy priorities of the GPEI and other public health authorities include the following:

• Maintaining coverage as the incidence of polio decreases and the importance of polio vaccination diminishes in public perception and the priorities of governments and funders
• Optimizing schedules and dosing to improve the immunogenicity and cost-effectiveness of polio vaccine programs
• Increasing types of vaccines and total vaccine production
• Reducing and eliminating the risk of WPV release from vaccine production

New and developing strategies include fractional dosing of IPV and aluminum-adjuvanted IPV, which require less antigen content per dose, thus extending the IPV vaccine supply and decreasing costs.[World Health Organization. Polio vaccines: WHO position paper – June 2022]

Extending Sabin-based IPV to more countries reduces the risk of accidental WPV release. Sabin-based IPV production requires less stringent biocontainment requirements than Salk IPV, lowering production costs. Meta-analysis showed no significant differences in seroconversion compared to Salk IPV.

Research continues into the development of new vaccines, including increasingly stable novel OPV2; novel OPV1 and OPV3 to eventually replace Sabin OPV; and other IPVs with a noninfectious process to reduce the accidental poliovirus reintroduction risk, including virus-like particle vaccines and messenger RNA vaccines.[World Health Organization. Polio eradication strategy 2022–2026: delivering on a promise]