Discussion
All WHO regions remain committed to measles elimination; however, no region has achieved and sustained elimination targets. Drops in MCV1 coverage and declines in surveillance performance that started or continued during the COVID-19 pandemic persisted in 2021.[5–7] Among regions, the Southeast Asia Region faced the largest decrease in MCV1 coverage (from 94% to 86%) between 2019 and 2021, and only the European Region maintained MCV1 coverage from 2020 to 2021. None of the WHO regions have recovered MCV1 or MCV2 coverage levels from 2019, which were still below the 95% coverage needed to achieve and sustain measles elimination.[8]
SIAs represent an opportunity to reach children with missing MCV doses from the routine immunization program and close immunity gaps.**** In 2021, the implementation of 25 campaigns that had been delayed because of COVID-19 indicates some pandemic recovery; however, 18 pending SIAs that had not yet been conducted as of December 2021 present a risk for measles outbreaks.
The observed decrease in measles incidence in 2020 and 2021 could reflect actual changes related to increased immunity after a 2017–2019 global resurgence of measles, reduced viral transmission associated with COVID-19 mitigation measures, limited detection resulting from surveillance system underperformance, or a combination of multiple factors.[1,2,9] Sensitivity of measles surveillance remained low in 2021, with continued low numbers of specimens received for laboratory testing and few countries achieving the surveillance sensitivity indicator. Sustained declines in surveillance not only affect the timely detection of cases and outbreaks but also undermine a program's ability to use measles as a tracer to highlight gaps in the overall immunization system.
The findings in this report are subject to at least three limitations. First, not all countries report complete, or any, data for SIAs and outbreak response activities; therefore, the numbers on these activities provided in this report could be underestimated. Second, the measles estimation model was updated this year, which limits comparability with estimates from previous years. Finally, the number of specimens submitted for genotyping represents a fraction of measles cases; hence, data presented in this report might not reflect the actual global distribution of genotypes.
Declining routine MCV coverage and delays in SIAs in 2021 left millions of children with zero or only 1 dose of MCV. In the absence of a high-performing surveillance system to promptly detect cases, a growing population of susceptible children is at risk for measles disease and outbreaks. In alignment with IA2030, the Measles and Rubella Strategic Framework 2021–2030†††† outlines strategies for countries to build robust, case-based surveillance for measles to detect immunity gaps and outbreaks, identify root causes of undervaccination, and develop targeted solutions, including catch-up immunization for those who missed routine immunization doses during the pandemic, to reach all children with 2 doses of MCV. Accelerating these measures will help regain historical progress toward regional measles elimination.
Acknowledgments
Country surveillance and immunization program staff members.
Morbidity and Mortality Weekly Report. 2022;71(47):1489-1495. © 2022 Centers for Disease Control and Prevention (CDC)
