Epidemiological Alert Detection of vaccine-derived poliovirus type 2 (VDPV2) in the United States: Implications for the Region of the Americas (21 July 2022)


Given the identification of a case of acute flaccid paralysis related to type 2 vaccinederived poliovirus in an unvaccinated individual from Rockland County, New York, United States of America, the Pan American Health Organization / World Health Organization (PAHO/WHO) reiterates to Member States to join efforts in order to maintain and strengthen surveillance for the detection of cases and achieve adequate vaccination coverage against poliomyelitis.

Situation summary

No cases of wild poliovirus have been detected in the countries and territories of the Region of the Americas in over 30 years. In 1994, the Americas became the first region in the world to be certified polio-free by the World Health Organization (WHO). The early detection of cases through the implementation of surveillance of acute flaccid paralysis (AFP) in children under 15 years of age and maintaining adequate polio vaccination coverage have been key to this achievement.

On 21 July 2022, as a result of surveillance conducted in the United States of America, the New York State Department of Health reported the identification of a case of paralytic poliomyelitis in an unvaccinated individual in Rockland County. Initial sequencing confirmed by the United States Centers for Disease Control and Prevention (U.S. CDC) indicates that this is a case of vaccine-derived poliovirus type 2 (VDPV2).1 The investigation is ongoing, further information will be shared as it becomes available.

On 10 June 2022, the Pan American Health Organization / World Health Organization (PAHO / WHO) published the Epidemiological Alert on the risk of poliovirus outbreak in the Region of the Americas, available at:, warning of the risk of the emergence of vaccine-derived poliovirus and urging Member States to implement effective measures to reduce the risk of outbreaks by maintaining high and homogeneous vaccination coverage, as well as having sensitive epidemiological surveillance systems allowing for timely detection and investigation of acute flaccid paralysis cases.

In recent years, polio vaccination rates have dropped considerably, even prior to the COVID19 pandemic, polio vaccination had fallen below the recommended 95% or greater coverage goal to prevent the reintroduction of the virus in this Region. During the pandemic - which has affected health services throughout the region, including routine vaccination - polio vaccination rates have continued to decline. In 2020, only 80% of children had received the third dose of polio vaccine necessary for full immunization, a decrease of 87% compared to 2019. If this trend in vaccination coverage continues, there is a high risk of outbreaks occurring after the importation of a virus (wild or vaccine-derived) or the emergence of poliovirus derived from the vaccine, and that these are not detected in time.