The risk of type 2 oral polio vaccine use in post-cessation outbreak response

Abstract

BackgroundWild type 2 poliovirus was last observed in 1999. The Sabin-strain oral polio vaccine type 2 (OPV2) was critical to eradication, but it is known to revert to a neurovirulent phenotype, causing vaccine-associated paralytic poliomyelitis. OPV2 is also transmissible and can establish circulating lineages, called circulating vaccine-derived polioviruses (cVDPVs), which can also cause paralytic outbreaks. Thus, in April 2016, OPV2 was removed from immunization activities worldwide. Interrupting transmission of cVDPV2 lineages that survive cessation will require OPV2 in outbreak response, which risks seeding new cVDPVs. This potential cascade of outbreak responses seeding VDPVs, necessitating further outbreak responses, presents a critical risk to the OPV2 cessation effort.MethodsThe EMOD individual-based disease transmission model was used to investigate OPV2 use in outbreak response post-cessation in West African populations. A hypothetical outbreak response in northwest Nigeria is modeled, and a cVDPV2 lineage is considered established if the Sabin strain escapes the response region and continues circulating 9 months post-response. The probability of this event was investigated in a variety of possible scenarios.ResultsUnder a broad range of scenarios, the probability that widespread OPV2 use in outbreak response (~2 million doses) establishes new cVDPV2 lineages in this model may exceed 50% as soon as 18 months or as late as 4 years post-cessation.ConclusionsThe risk of a cycle in which outbreak responses seed new cVDPV2 lineages suggests that OPV2 use should be managed carefully as time from cessation increases. It is unclear whether this risk can be mitigated in the long term, as mucosal immunity against type 2 poliovirus declines globally. Therefore, current programmatic strategies should aim to minimize the possibility that continued OPV2 use will be necessary in future years: conducting rapid and aggressive outbreak responses where cVDPV2 lineages are discovered, maintaining high-quality surveillance in all high-risk settings, strengthening the use of the inactivated polio vaccine as a booster in the OPV2-exposed and in routine immunization, and gaining access to currently inaccessible areas of the world to conduct surveillance.Electronic supplementary materialThe online version of this article (10.1186/s12916-017-0937-y) contains supplementary material, which is available to authorized users.

Assessing the Risk of Vaccine-derived Outbreaks After Reintroduction of Oral Poliovirus Vaccine in Postcessation Settings

“…These findings may be important in risk assessment surrounding OPV use and for focusing surveillance for cVDPV emergence. Our findings concerning the overall probability of cVDPV emergence are consistent with those of a 2017 study examining the possibility of outbreak responses seeding cVDPV2 after cessation of OPV2 [ 18 ]. That study estimated this probability to exceed 50% as soon as 18 months after cessation, an estimate supported under the highest risk conditions by our model.…”

“…Ten thousand simulations were performed, and the cumulative incidence of infections and the duration of persistent transmission for all those simulations were presented. We defined cVDPV risk as the proportion of simulations in which Sabin virus persisted for >9 months after introduction [ 18 ].…”

Evolving epidemiology of poliovirus serotype 2 following withdrawal of the serotype 2 oral poliovirus vaccine

“…We conclude that the GPEI are in a paradoxical situation: on the one hand, it is not currently possible to control the outbreaks without inducing intestinal mucosal immunity through mOPV2 use, but on the other hand, the use of mOPV2 is generating VDPV2. The risk of VDPV2 circulation is increasing over time, as the immunity of the global population rapidly decreases (5).…”

“…Therefore, the method to control VDPV2 transmission is through vaccination campaigns with the monovalent OPV2 (mOPV2) (4). However, any use of mOPV2 carries the risk of seeding more VDPV2 (5).…”

Cold chain and virus‐free oral polio booster vaccine made in lettuce chloroplasts confers protection against all three poliovirus serotypes

“…Continued use of serotype 2 in oral polio vaccine (OPV) led to 683 cases of polio caused by circulation of vaccine-derived poliovirus type 2 (cVDPV2) between 2000and 2014(McCarthy et al, 2017. Therefore, WHO Global Polio Eradication Initiative recommended withdrawal of the type 2 component (OPV2) in April 2016 and replacing bivalent OPV (bOPV) in all 155 countries and territories that had used OPV in 2015 (Holmes et al, 2017;Ramirez Gonzalez et al, 2017).…”