Two-year duration of immunity of inactivated poliovirus vaccine: A follow-up study in Pakistan in 2020

Document Type



Paediatrics and Child Health


This was a follow-up study conducted in 2020 assessing changes in levels of type 2 poliovirus-neutralizing antibodies two years post-immunization in children who received inactivated poliovirus vaccine (IPV) in Karachi, Pakistan. Unexpectedly, the findings revealed an increase in seroprevalence of type 2 antibodies from 73.1% to 81.6% one and two years after IPV, respectively. The increase in type 2 immunity could result from the intensive transmission of circulating vaccine-derived poliovirus type 2 (cVDPV2) in Karachi during the second year of IPV administration. This study suggests that the cVDPV2 outbreak detected in Pakistan infected large proportions of children in Karachi. Clinical Trial Registration NCT03286803.


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Publication (Name of Journal)

The Journal of Infectious Diseases