What is vaccine-associated paralytic polio (VAPP)?

Vaccine-Associated Paralytic Polio (VAPP)

Vaccine-associated paralytic polio (VAPP) is a rare but serious adverse event characterized by paralysis that occurs as a result of the oral poliovirus vaccine (OPV), caused by reversion of the attenuated vaccine virus to a more neurovirulent form. 1

Definition and Mechanism

• VAPP occurs when the live attenuated poliovirus in OPV reverts to a more neurovirulent form, causing paralysis that is clinically indistinguishable from paralytic poliomyelitis caused by wild poliovirus 2
• The paralysis typically affects one or more limbs with reduced or absent tendon reflexes and no sensory loss 3
• The condition can result in permanent paralysis and, in rare cases, death 1

Epidemiology and Risk Factors

• VAPP can occur in both vaccine recipients and in contacts of vaccinees who are exposed to the vaccine-derived virus 1
• The overall risk of VAPP is approximately one case per 2.6 million OPV doses distributed 4
• The risk is significantly higher with the first dose of OPV (approximately one case per 520,000 first doses) compared to subsequent doses (one case per 12.3 million subsequent doses) 4
• Risk varies by country income level:
  • In low-income countries, most cases occur in individuals who have received multiple OPV doses (63%) 5
  • In middle and high-income countries, most cases occur after the first OPV dose or in unvaccinated contacts (81%) 5

High-Risk Populations

• Immunodeficient individuals are at substantially increased risk for VAPP 1
• Persons with congenital immunodeficiency disorders (severe combined immunodeficiency syndrome, agammaglobulinemia, hypogammaglobulinemia) 1
• Persons with altered immune systems due to:
  • Malignant diseases (leukemia, lymphoma, generalized malignancy) 1
  • Immunosuppressive therapy (corticosteroids, alkylating drugs, antimetabolites, radiation) 1
  • HIV infection 1
• Adults have a slightly higher risk of VAPP than children 1

Clinical Presentation and Diagnosis

• Onset of paralysis typically occurs 4-40 days after OPV administration in recipients 6
• In contacts of vaccinees, paralysis can occur within approximately 4-6 weeks after exposure 1
• Clinical features include:
  • Acute flaccid paralysis 2
  • Residual weakness persisting 60 days after onset 6
  • Isolation of vaccine-related poliovirus from stool samples 2, 6
• Paralysis may be localized to the limb where other vaccines were administered concurrently 3

Prevention and Management

• The United States switched from OPV to inactivated poliovirus vaccine (IPV) in 2000 specifically to eliminate the risk of VAPP while maintaining high levels of protection against wild polioviruses 1
• IPV does not cause VAPP because it contains killed virus that cannot revert to neurovirulence 1
• For individuals at higher risk of exposure to wild poliovirus (travelers to endemic areas, healthcare workers), IPV is preferred over OPV due to the risk of VAPP 1
• OPV should not be administered to immunodeficient individuals or their household contacts; IPV is recommended instead 1
• If OPV is inadvertently given to a household contact of an immunodeficient person:
  • The OPV recipient should avoid close contact with the immunodeficient person for 4-6 weeks 1
  • If separation is not feasible, rigorous hygiene practices should be implemented 1

Global Burden and Future Directions

• The global annual burden of VAPP is estimated at 399-498 cases 5
• The burden is now concentrated in lower-income countries that still use OPV 5
• The planned universal introduction of IPV is expected to decrease the global VAPP burden by 80-90% 5

Reporting and Compensation

• In the United States, VAPP cases must be reported to the Vaccine Adverse Events Reporting System (VAERS) 1
• The National Vaccine Injury Compensation Program provides potential compensation for VAPP cases occurring in:
  • OPV recipients (within 30 days of vaccination) 1
  • Contacts of OPV vaccinees (no specific time frame) 1
  • Immunodeficient persons (within 6 months) 1