Outbreak response strategies with type 2-containing oral poliovirus vaccines

Looking back at prospective modeling of outbreak response strategies for managing global type 2 oral poliovirus vaccine (OPV2) cessation

“…We characterize the performance of oSIAs using true coverage and repeatedly missed probability (P RM ) inputs, the latter of which accounts for missing the same children between successive rounds. Consistent with observed performance, the oSIA intensity in the model varies for different subpopulations, ranging from 15% true coverage and 95% P RM to 80% true coverage and 70% P RM (27,28,(46)(47)(48)(49)52). The RC uses mOPV2 as the primary vaccine for type 2 oSIAs for the entire time horizon as a modeling benchmark for comparisons (49).…”

“…Applying the integrated model with assumptions that reflect actual choices and performance, we previously modeled a deterministic run-up until December 31, 2021 and ran 100 prospective stochastic iterations for the period of January 1, 2022 to December 31, 2026, which we refer to as the current reference case (RC) for the trajectory of the GPEI (49). The current RC, as observed after OPV2 cessation, uses inputs for RI and SIAs as they occurred through December 31, 2021 (49) and assumes that prospective preventive SIAs (pSIAs) occur based on recent and current GPEI strategic plans (43,45). With respect to the oSIAs, the RC assumes characteristics for prospective oSIAs consistent with recent performance (Table 1, rightmost column) (27).…”

“…With respect to the oSIAs, the RC assumes characteristics for prospective oSIAs consistent with recent performance (Table 1, rightmost column) (27). Specifically, prospective oSIAs in the current RC target children <5 years of age, start 45 days after detection, and include 2 rounds of mOPV2 separated by 30 days, and perform 2 additional rounds after detection of breakthrough transmission (27,49). The scope of the modeled prospective oSIAs includes the outbreak subpopulation alone for subpopulations with a type 1 wild poliovirus (WPV1) basic reproduction number (R 0 ) <10 (most subpopulations), or the outbreak subpopulation and its four worst-performing neighbor subpopulations within the same block when WPV1 R 0 ≥ 10 (49).…”

“…With anticipation that nOPV2 would replace mOPV2 by July 2021 (44), integrated modeling explored how using nOPV2 instead of mOPV2 might change the expected endgame trajectory for type 2 poliovirus transmission (46). After the COVID-19 pandemic disrupted global activities, further modeling characterized the impacts of these disruptions on the polio endgame trajectory and the expected impacts of using of nOPV2 for outbreak response instead of or in addition to mOPV2 (47)(48)(49). Although the use of nOPV2 promises greater genetic stability (50), which means lower risks of evolving to cause new outbreaks while preserving some mucosal immunological benefits induced by OPV, all of these studies highlighted the need for improved oSIA performance (47)(48)(49).…”

“…After the COVID-19 pandemic disrupted global activities, further modeling characterized the impacts of these disruptions on the polio endgame trajectory and the expected impacts of using of nOPV2 for outbreak response instead of or in addition to mOPV2 (47)(48)(49). Although the use of nOPV2 promises greater genetic stability (50), which means lower risks of evolving to cause new outbreaks while preserving some mucosal immunological benefits induced by OPV, all of these studies highlighted the need for improved oSIA performance (47)(48)(49). These studies repeated the message that vaccine failure was not the problem, and that OPV cessation and polio eradication remain off track due to the failure to vaccinate (4, 34).…”