UPDATE: In July 2022, CDC was notified of a case of polio caused by vaccine-derived poliovirus type 2 (VDPV2) in an unvaccinated individual from Rockland County, New York, and is consulting with the New York State Department of Health on their investigation. Public health experts are working to understand how and where the individual was infected and provide protective measures, such as vaccination services to the community to prevent the spread of polio to under- and unvaccinated individuals.
What is a vaccine-derived poliovirus?
A vaccine-derived poliovirus (VDPV) is a strain related to the weakened live poliovirus contained in oral polio vaccine (OPV). If allowed to circulate in under- or unimmunized populations for long enough, or replicate in an immunodeficient individual, the weakened virus can revert to a form that causes illness and paralysis.
OPV is a safe and effective vaccine that contains a combination of one, two, or three strains of live, weakened poliovirus, and is given in the form of oral drops. OPV has been instrumental in eradicating wild polioviruses around the world, including in the United States, because it stops the spread of the virus by inducing immunity in the gut. VDPVs emerge when not enough people are vaccinated against polio, and the weakened strain of the poliovirus from OPV spreads among under-immunized populations.
The United States has used inactivated poliovirus vaccine (IPV) exclusively since 2000. IPV is given as an injection in the leg or arm, depending on the person’s age and protects against paralytic disease caused by any type of poliovirus, including VDPV.
Where do vaccine-derived polioviruses (VDPVs) come from, and should I be concerned if there is a case in the United States?
VDPVs can cause outbreaks in places where vaccine coverage is low. In addition, people with certain immunodeficiency disorders can shed the virus for long periods of time, during which the virus can continue to change and can infect an unvaccinated person. Because OPV has not been used in the United States since 2000 and vaccine coverage with IPV is high, it is unlikely that any VDPV would become widespread in the United States.
Polio vaccination protects people against naturally occurring polioviruses and VDPVs. Continuing to achieve high IPV vaccination coverage in the United States is the best way to keep the country polio-free and prevent importations of the virus. In addition, access to clean water, good hand hygiene habits, modern sewage systems and wastewater management further prevent germs, including viruses like poliovirus, from spreading. Polio eradication remains a CDC global health priority to protect children today and all future generations from this preventable disease.