Impact of Supplementary Immunization Activities using Novel Oral Polio Vaccine Type 2 during a Large outbreak of Circulating Vaccine-Derived Poliovirus in Nigeria

BACKGROUND: Novel oral poliovirus vaccine (OPV) type 2 (nOPV2) has been made available for outbreak response under an emergency use listing authorization based on supportive clinical trial data. Since 2021 more than 350 million doses of nOPV2 were used for control of a large outbreak of circulating vaccine-derived poliovirus type 2 (cVDPV2) in Nigeria. METHODS: Using a bayesian time-series susceptible-infectious-recovered model, we evaluate the field effectiveness of nOPV2 immunization campaigns in Nigeria compared with campaigns using monovalent OPV type 2 (mOPV2). RESULTS: We found that both nOPV2 and mOPV2 campaigns were highly effective in reducing transmission of cVDPV2, on average reducing the susceptible population by 42% (95% confidence interval, 28-54%) and 38% (20-51%) per campaign, respectively, which were indistinguishable from each other in this analysis (relative effect, 1.1 .7-1.9). Impact was found to vary across areas and between immunization campaigns. CONCLUSIONS: These results are consistent with the comparable individual immunogenicity of nOPV2 and mOPV2 found in clinical trials but also suggest that outbreak response campaigns may have small impacts in some areas requiring more campaigns than are suggested in current outbreak response procedures.