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Background Global withdrawal of serotype-2 oral poliovirus vaccine (OPV2) took place in April 2016. This marked a milestone in global polio eradication and was a public health intervention of unprecedented scale, affecting 155 countries. Achieving high levels of serotype-2 population immunity before OPV2 withdrawal was critical to avoid subsequent outbreaks of serotype-2 vaccine-derived polioviruses (VDPV2s). Methods and Findings In August 2015, we estimated vaccine-induced population immunity against serotype-2 poliomyelitis for 1 January 2004–30 June 2015 and produced forecasts for April 2016 by district in Nigeria and Pakistan. Population immunity was estimated from the vaccination histories of children 70% population immunity among children, Isobel Mary Blake and colleagues use spatio-temporal modelling of surveillance data to estimate population immunity leading up to the global withdrawal of serotype-2 oral poliovirus vaccine., Author Summary Why Was This Study Done? The Global Polio Eradication Initiative’s strategic plan includes the global withdrawal of all oral poliovirus vaccines (OPVs) because they can result, albeit rarely, in outbreaks of poliomyelitis caused by vaccine-derived poliovirus (VDPV). Serotype-2 OPV (OPV2) was withdrawn from trivalent OPV in all 155 countries using this vaccine in April 2016, as the last naturally occurring case of polio caused by serotype-2 wild poliovirus was reported in 1999. Strategies to minimise the risk of serotype-2 VDPVs during the period leading up to OPV2 withdrawal were required. What Did the Researchers Do and Find? To assess the risks associated with OPV2 withdrawal, we estimated population immunity against poliomyelitis caused by serotype 2 in children under three years old in eight countries (including the two highest risk countries: Nigeria and Pakistan). We found substantial improvements in serotype-2 population immunity over the last five years in most countries, although immunity in parts of northeastern Nigeria and northwestern Pakistan remained relatively low. Projections of immunity through April 2016 were used to explore the impact of alternative immunisation campaigns including the use of inactivated poliovirus vaccine. What Do These Findings Mean? An increased number of campaigns with trivalent OPV and IPV led to improvements in serotype-2 immunity, thereby minimising the risk of serotype-2 VDPVs associated with OPV2 withdrawal in April 2016. These immunity estimates and projections were used to support the decision by the World Health Organization Strategic Advisory Group of Experts on Immunization to proceed with OPV2 withdrawal.

Additional file 1 : Table S1. A detailed timeline of key events and policy changes throughout the COVID-19 outbreak in South Korea. Table S2. Most recent case definitions for suspected cases and patients under investigation for COVID-19 infection (Source: MOHW, last updated June 25th). Section 2. Contact tracing of individuals – detailed protocol for contact tracing in South Korea. Figure S1. A regional breakdown of the change in epidemiological links of confirmed cases over time. Table S3. The prior means and standard deviations explored in our sensitivity analysis of the Rt estimates.

Additional file 1 : Table S1. A detailed timeline of key events and policy changes throughout the COVID-19 outbreak in South Korea. Table S2. Most recent case definitions for suspected cases and patients under investigation for COVID-19 infection (Source: MOHW, last updated June 25th). Section 2. Contact tracing of individuals – detailed protocol for contact tracing in South Korea. Figure S1. A regional breakdown of the change in epidemiological links of confirmed cases over time. Table S3. The prior means and standard deviations explored in our sensitivity analysis of the Rt estimates.