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Estimates of national immunization coverage are crucial for guiding policy and decision-making in national immunization programs and setting the global immunization agenda. WHO and UNICEF estimates of national immunization coverage (WUENIC) are produced annually for various vaccine-dose combinations and all WHO Member States using information from multiple data sources and a deterministic computational logic approach. This approach, however, is incapable of characterizing the uncertainties inherent in coverage measurement and estimation. It also provides no statistically principled way of exploiting and accounting for the interdependence in immunization coverage data collected for multiple vaccines, countries and time points. Here, we develop Bayesian hierarchical modeling approaches for producing accurate estimates of national immunization coverage and their associated uncertainties. We propose and explore two candidate models: a balanced data single likelihood (BDSL) model and an irregular data multiple likelihood (IDML) model, both of which differ in their handling of missing data and characterization of the uncertainties associated with the multiple input data sources. We provide a simulation study that demonstrates a high degree of accuracy of the estimates produced by the proposed models, and which also shows that the IDML model is the better model. We apply the methodology to produce coverage estimates for select vaccine-dose combinations for the period 2000-2019. A contributed R package {\tt imcover} implementing the No-U-Turn Sampler (NUTS) in the Stan programming language enhances the utility and reproducibility of the methodology., Comment: 31 pages (main), 4 figures

Additional file 1.

Background The SARS-CoV-2 pandemic has revealed the vulnerability of immunisation systems worldwide, although the scale of these disruptions has not been described at a global level. This study aims to assess the impact of COVID-19 on routine immunisation using triangulated data from global, country-based, and individual-reported sources obtained during the pandemic period. Methods This report synthesised data from 170 countries and territories. Data sources included administered vaccine-dose data from January to December, 2019, and January to December, 2020, WHO regional office reports, and a WHO-led pulse survey administered in April, 2020, and June, 2020. Results were expressed as frequencies and proportions of respondents or reporting countries. Data on vaccine doses administered were weighted by the population of surviving infants per country. Findings A decline in the number of administered doses of diphtheria–pertussis–tetanus-containing vaccine (DTP3) and first dose of measles-containing vaccine (MCV1) in the first half of 2020 was noted. The lowest number of vaccine doses administered was observed in April, 2020, when 33% fewer DTP3 doses were administered globally, ranging from 9% in the WHO African region to 57% in the South-East Asia region. Recovery of vaccinations began by June, 2020, and continued into late 2020. WHO regional offices reported substantial disruption to routine vaccination sessions in April, 2020, related to interrupted vaccination demand and supply, including reduced availability of the health workforce. Pulse survey analysis revealed that 45 (69%) of 65 countries showed disruption in outreach services compared with 27 (44%) of 62 countries with disrupted fixed-post immunisation services. Interpretation The marked magnitude and global scale of immunisation disruption evokes the dangers of vaccine-preventable disease outbreaks in the future. Trends indicating partial resumption of services highlight the urgent need for ongoing assessment of recovery, catch-up vaccination strategy implementation for vulnerable populations, and ensuring vaccine coverage equity and health system resilience. Funding US Agency for International Development.

Analyzing immunization coverage data is crucial to guide decision-making in national immunization programs and monitor global initiatives such as the Immunization Agenda 2030. We aimed to assess the quality of reported child immunization coverage data for 194 countries over 20 years. We analyzed child immunization coverage as reported to the World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF) between 2000–2019 by all WHO Member States for Bacillus Calmette-Guérin (BCG) vaccine birth dose, first and third doses of diphtheria-tetanus-pertussis-containing vaccine (DTP1, DTP3), and first dose of measles-containing vaccine (MCV1). We assessed completeness, consistency, integrity, and congruence and assigned data quality flags in case anomalies were detected. Generalized linear mixed-effects models were used to estimate the probability of flags worldwide and for different country groups over time. The probability of data quality flags was 18.2% globally (95% confidence interval [CI] 14.8–22.3). The lowest probability was seen in South-East Asia (6.3%, 3.3–11.8, p = 0.002), the highest in the Americas (29.7%, 22.7–37.9, p < 0.001). The probability of data quality flags declined by 5.1% per year globally (3.2–7.0, p < 0.001). The steepest decline was seen in Africa (-9.6%, -13.0 to -5.8, p < 0.001), followed by Europe (-5.4%, -9.2 to -1.6, p = 0.0055), and the Americas (-4.9%, -9.2 to -0.6, p = 0.026). Most country groups showed a statistically significant decline, and none had a statistically significant increase. Over the past two decades, the quality of global immunization coverage data appears to have improved. However, progress has not been universal. The results highlight the need for joint efforts so that all countries collect, report, and use high-quality data for action in immunization.

Household surveys are frequently used as means of vaccination coverage measurement, but obtaining accurate survey estimates present several challenges. In 2015, the World Health Organization (WHO) released a working draft of its updated Vaccination Coverage Survey Reference Manual that moved well beyond the traditional Expanded Program on Immunization (EPI) survey design. In April 2017, WHO convened a four-day meeting, to review lessons learned using the updated manual and to define an agenda for operational research about vaccination coverage surveys. About 70 stakeholders, including EPI managers and participants from 10 countries that have used the updated Survey Manual, survey experts, statisticians, partners, representatives from WHO regional offices and headquarters, and providers of technical assistance discussed methodological issues from sampling to accurately ascertaining a person’s vaccination status, optimizing data collection and data management and conducting appropriate analyses. Participants also discussed data sharing and how to best survey data for immunization decision-making. The lessons learned from the use of the updated WHO Survey Manual related mainly to operational issues to implement better quality vaccination coverage surveys. It resulted in a list of 23 recommendations for WHO, donors and partners, immunization programs, and household surveys that collect immunization data. Similarly, 14 research topics, categorized in six themes (overall survey conduction, sampling, vaccination ascertainment, data collection, data analysis and use, and inclusion of questions on knowledge, attitudes and practices) were prioritized. Top areas of further work included improving our understanding of the accuracy of caregiver recall when documented evidence of vaccination is not available, improving engagement and coordination between immunization programs and entities conducting multi-purpose household surveys such as Demographic and Health Survey and Multiple Cluster Indicator Survey, improving mechanisms for sharing vaccination survey datasets and documentation, and making better use of survey results to translate data into knowledge for decision-making. This manuscript summarizes the meeting proceedings and provides an update of actions taken by WHO since this meeting.

In 2012, the World Health Assembly endorsed the Global Vaccine Action Plan with the objective to eliminate measles in four World Health Organization (WHO) regions by 2015. Member states of all six WHO regions have adopted measles elimination goals. In 2010, the World Health Assembly established three milestones for 2015: 1) increase routine coverage with the first dose of measles-containing vaccine (MCV1) for children aged 1 year to ≥90% nationally and ≥80% in every district; 2) reduce global annual measles incidence to5 cases per million; and 3) reduce global measles mortality by 95% from the 2000 estimate. This report updates the 2000-2012 report and describes progress toward global control and regional measles elimination during 2000-2013. During this period, annual reported measles incidence declined 72% worldwide, from 146 to 40 per million population, and annual estimated measles deaths declined 75%, from 544,200 to 145,700. Four of six WHO regions have established regional verification commissions (RVCs); in the European (EUR) and Western Pacific regions (WPR), 19 member states successfully documented the absence of endemic measles. Resuming progress toward 2015 milestones and elimination goals will require countries and their partners to raise the visibility of measles elimination, address barriers to measles vaccination, and make substantial and sustained additional investments in strengthening health systems.

In 2010, the World Health Assembly established three milestones toward global measles eradication to be reached by 2015: 1) increase routine coverage with the first dose of measles-containing vaccine (MCV1) for children aged 1 year to ≥90% nationally and ≥80% in every district, 2) reduce and maintain annual measles incidence at5 cases per million, and 3) reduce measles mortality by 95% from the 2000 estimate. After the adoption by member states of the South-East Asia Region (SEAR) of the goal of measles elimination by 2020, elimination goals have been set by member states of all six World Health Organization (WHO) regions, and reaching measles elimination in four WHO regions by 2015 is an objective of the Global Vaccine Action Plan (GVAP). This report updates the previous report for 2000-2011 and describes progress toward global control and regional elimination of measles during 2000-2012. During this period, increases in routine MCV coverage, plus supplementary immunization activities (SIAs) reaching 145 million children in 2012, led to a 77% decrease worldwide in reported measles annual incidence, from 146 to 33 per million population, and a 78% decline in estimated annual measles deaths, from 562,400 to 122,000. Compared with a scenario of no vaccination, an estimated 13.8 million deaths were prevented by measles vaccination during 2000-2012. Achieving the 2015 targets and elimination goals will require countries and their partners to raise the visibility of measles elimination and make substantial and sustained additional investments in strengthening health systems.

Pneumococcal conjugate vaccines (PCVs) are safe and effective for reducing illness and deaths caused by Streptococcus pneumoniae. Recommendations for PCV use from the World Health Organization (WHO) and funding from the GAVI Alliance have resulted in an increase in PCV introductions into national immunization programs, especially in lower-income countries. Additionally, new formulations that cover more serotypes commonly causing disease in lower- and middle-income countries have become available. This report uses WHO data from 2000-2012, stratified by country disease burden characteristics and World Bank country income groups, to describe global progress in PCV introduction. As of December 2012, a total of 86 (44%) WHO member states have added PCV to the routine infant immunization schedule of their national immunization programs; among those, 23 have introduced PCV with GAVI Alliance support. PCV introduction among WHO member states was most common in the Americas Region (60% of member states), followed by the Eastern Mediterranean Region (50%), European Region (49%), African Region (41%), and Western Pacific Region (33%); none of 11 WHO member states in the South-East Asia Region have introduced PCV. Proportions of low- and middle-income countries with PCV introductions were similar. The proportion of the world's birth cohort living in countries with PCV in national immunization programs increased from 1% in 2000 to 31% in 2012. These findings suggest that efforts to increase PCV introduction and use globally are succeeding; however, gaps in PCV use remain in Asia and countries with large birth cohorts, where concerted efforts should be focused.