High population immunity is an indicator of the decline in serotype 2 Sabin vaccine (Sabin-2) poliovirus after serotype 2 oral poliovirus vaccine (OPV2) withdrawal, and has restricted the incidence of serotype 2 vaccine-derived poliovirus (VDPV2) to areas known to be at high risk for transmission, according to a study published in The New England Journal of Medicine.1

To completely eradicate polio, oral poliovirus vaccine (OPV) itself must be withdrawn to prevent outbreaks of vaccine-derived poliovirus (VDPV), which occurs in approximately 1 outbreak per 500 million persons vaccinated.2 In April 2016, the World Health Organization recommended that the global withdrawal of OPV begin by removing OPV2 from trivalent OPV and replacing it with a bivalent OPV containing serotypes 1 and 3 to prevent further emergence of circulating VDPV2.3,4

Researchers analyzed global surveillance data on the detection of Sabin-2 poliovirus and VDPV2 in the stool samples of 495,035 children with acute flaccid paralysis in 188 countries and in 8528 sewage samples from 4 countries that are at high risk for transmission. Investigators found that the prevalence of Sabin-2 poliovirus in stool samples declined from 3.9% (95% CI, 3.5-4.3) at the time of OPV2 withdrawal to .2% (95% CI, .1-2.7) at 2 months after withdrawal, and the detection in sewage samples decreased from 71.0% (95% CI, 61.0-80.0) to 13.0% (95% CI, 8.0-20.0) during the same time period. However, 12 months after OPV2 withdrawal, Sabin-2 poliovirus continued to be detected, though in a continued decreasing trend, in stool samples (<.1%; 95% CI, <.1-.1) and in sewage samples (8.0%; 95% CI, 5.0-8.0) because of the use of OPV2 in response to VDPV2 outbreaks. Of note, 9 outbreaks were reported after OPV2 withdrawal, which were associated with low rates of routine vaccinations, and low levels of population immunity. Therefore, prevention of VDPV2 outbreaks in areas known to be at high risk for transmission is critical to the success of polio eradication.

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The researchers concluded that their findings “We show here that serotype 2 vaccine poliovirus disappeared rapidly after OPV2 withdrawal, but in a small number of high-risk locations it has persisted because of the use of monovalent OPV2 in response to VDPV outbreaks or unplanned administration of trivalent OPV from old stocks.” The authors also note that, “our findings provide evidence that supports the planned withdrawal of bivalent OPV after eradication of wild polioviruses is confirmed, provided that a high level of immunity and effective surveillance is maintained in high-risk areas.”1


  1. Blake IM, Pons‑Salort M, Molodecky NA, et al. Type 2 poliovirus detection after global withdrawal of trivalent oral vaccine. N Engl J Med. 2018;379:834-845.
  2. Alexander LN, Seward JF, Santibanez TA, et al. Vaccine policy changes and epidemiology of poliomyelitis in the United States. JAMA. 2004;292:1696-1701.
  3. Meeting of the Strategic Advisory Group of Experts on Immunization, November 2012 — conclusions and recommendations. Wkly Epidemiol Rec. 2013;88:1-16.
  4. Hampton LM, Farrell M, Ramirez-Gonzalez A, et al; Immunization Systems Management Group of the Global Polio Eradication Initiative. Cessation of trivalent oral poliovirus vaccine and introduction of inactivated poliovirus vaccine — worldwide, 2016. MMWR Morb Mortal Wkly Rep. 2016;65:934-938.

This article originally appeared on Infectious Disease Advisor