The Differential Impact of Oral Poliovirus Vaccine Formulation Choices on Serotype-Specific Population Immunity to Poliovirus Transmission
by Kimberly M. Thompson and Radboud J. Duintjer Tebbens, BMC Infectious Diseases 2015; 15:376, doi:10.1186/s12879-015-1116-4.

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What are the study’s main findings?
What are the study’s main recommendations?
Background on polio

What are the study’s main findings?

• Data from clinical trials suggest that the difference in cumulative seroconversion rates of the serotype 1 and 3 components of the bivalent oral poliovirus vaccine (bOPV) and those of the trivalent oral polioviruses vaccine (tOPV) decrease substantially with repeated doses.
• Children still susceptible to serotype 2 polioviruses will experience relatively greater rates of serotype 2 seroconversion if given tOPV, while children still susceptible to serotype 1 and/or 3 polioviruses will experience relatively greater rates of serotypes 1 and/or 3 seroconversion. Thus, repeated tOPV vaccinations will address immunity gaps for all 3 serotypes, while bOPV vaccinations will not address serotype 2 immunity gaps.
• Building on prior modeling of poliovirus transmission in northwest Nigeria (extended to explore the role of expanded age groups for supplemental immunization activities (SIAs), strategies to increase population immunity, the potential for undetected circulation, and trade-offs associated with different immunization options), we found a small effect on population immunity to serotype 1 and serotype 3 transmission of using only tOPV compared to only bOPV for 9 annual supplemental immunization activities (SIAs). However, the number of SIAs that contain tOPV greatly affected population immunity to serotype 2 transmission, with outbreaks of serotype 2 circulating vaccine-derived poliovirus (cVDPV2) occurring for 3 or fewer annual tOPV SIAs.
• Using an integrated global model of long-term poliovirus risk management policies, we found almost no impact of tOPV intensification or exclusive tOPV use for SIAs compared to more emphasis on bOPV SIAs on population immunity to serotype 1 and 3 transmission in different populations. However, with increased emphasis on bOPV SIAs at the expense of tOPV SIAs, we found lower population immunity to serotype 2 transmission, leading to cVDPV2 outbreaks after the planned globally-coordinated cessation of serotype 2-containing OPV (OPV2 cessation).
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• Countries that need to conduct SIAs to supplement routine immunization should prioritize the use of tOPV for those SIAs until coordinated OPV2 cessation to maintain high population immunity to transmission of all 3 serotypes and minimize the risk of cVDPV2 outbreaks after OPV2 cessation.
• In the run up to OPV2 cessation or as a contingency in the event of delayed OPV2 cessation, countries and the Global Polio Eradication Initiative should order sufficient tOPV to conduct all needed tOPV SIAs until coordinated OPV2 cessation.
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