Global Impact of Mass Vaccination Campaigns on Circulating Type 2 Vaccine-Derived Poliovirus Outbreaks: An Interrupted Time-Series Analysis

Figures

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  Figure 1.. Summary of cVDPV2 incidence, prevalence, and outbreak response in World Health Organization African, Eastern Mediterranean, European, South-East Asian, and Western Pacific Regions. A, Monthly cVDPV2 poliomyelitis cases, 1 January 2016 to 1 November 2023. B, Monthly prevalence of cVDPV2 detection in environmental surveillance (error bars show 95% binomial confidence interval), 1 January 2016 to 1 November 2023. C, Map of countries implementing mOPV2, nOPV2, or tOPV SIAs, 1 May 2016 to 1 November 2023. D, Approximate number of monthly doses of mOPV2, nOPV2, and tOPV delivered in SIAs, 1 May 2016 to 1 November 2023 (estimated aged under 5 years population in targeted regions). Abbreviations: cVDPV2, circulating vaccine-derived type 2 poliomyelitis; mOPV2, monovalent type 2 oral poliovirus vaccine; nOPV2, novel type 2 oral poliovirus vaccine; SIA, supplementary immunization activities; tOPV, trivalent type 2 oral poliovirus vaccine.

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  Figure 2.. Log-linear per-SIA impact of mOPV2 and nOPV2 on (A) cVDPV2 poliomyelitis incidence (RR) and (B) prevalence in ES (OR), adjusting for immunity before the first SIA. Points show central RR or OR estimate and error bars show 95% CI. Countries are ordered from top to bottom by those included in both nOPV2 and mOPV2 analysis, nOPV2 only, and mOPV2 only, and then by magnitude of RR or OR central estimate. Countries with an asterisk (*) and dotted error bars have zero cases or detections following SIAs. Countries with caret (^) and dashed error bars have zero cases or detections before an SIA. Role of immunity: RR, 1.17 (95% CI, 1.12–1.21); OR, 1.12 (95% CI, 1.10–1.14) per 10% absolute increase. See Supplementary Tables 7 and 8 for a tabular representation of these results. Abbreviations: CAR, Central African Republic; CI, confidence interval; cVDPV2, circulating vaccine-derived type 2 poliomyelitis; DRC, Democratic Republic of Congo; ES, environmental surveillance; mOPV2, monovalent type 2 oral poliovirus vaccine; nOPV2, novel type 2 oral poliovirus vaccine; OR, odds ratio; RR, risk ratio; SIA, supplementary immunization activities.

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  Figure 3.. Log-linear per-SIA impact of mOPV2 and nOPV2 on cVDPV2 poliomyelitis incidence (RR) and prevalence in ES (OR) in Nigeria (A) and DRC (C) by subnational region (maps in (B) and (D), respectively), adjusting for immunity before the SIA. Points show central RR or OR estimate and vertical lines show 95% CI. Regions with an asterisk (*) and dotted error bars have zero cases or detections following SIAs. Regions with caret (^) and dashed error bars have zero cases or detections before an SIA. Role of immunity: RR, 1.17 (95% CI, 1.12–1.22); OR, 1.08 (95% CI, 1.06–1.11) per 10% absolute increase. See Supplementary Tables 9 and 10 for a tabular representation of these results. Abbreviations: CI, confidence interval; cVDPV2, circulating vaccine-derived type 2 poliomyelitis; DRC, Democratic Republic of Congo; ES, environmental surveillance; mOPV2, monovalent type 2 oral poliovirus vaccine; nOPV2, novel type 2 oral poliovirus vaccine; OR, odds ratio; RR, risk ratio; SIA, supplementary immunization activities.

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  Figure 4.. District-level LQAS results for nOPV2 and mOPV2 district SIAs included in interrupted time-series analysis (9 May 2016 to 1 November 2023) by country (A), by vaccine (B), and by vaccine in Nigeria (C). LQAS is a standardized cluster survey method designed to detect whether coverage at the district level has likely exceeded (pass) or not exceeded (fail) a fixed threshold of 90%. Where multiple clusters of settlements are sampled and 1 or more passes and 1 or more fails, this is defined as a mixed result. Abbreviations: CAR, Central African Republic; DRC, Democratic Republic of Congo; LQAS, lot quality assurance sampling; mOPV2, monovalent type 2 oral poliovirus vaccine; nOPV2, novel type 2 oral poliovirus vaccine; SIA, supplementary immunization activities.