While 22 outbreaks were reported in 17 states during 2019, the majority of measles cases occurred in a pair of outbreaks that started in late 2018, one in New York City and the other in New York state. Theses two outbreaks, which occurred in underimmunized, close-knit communities, accounted for 934 (75%) of the 2019 total. An additional six outbreaks in similar communities accounted for nearly half of the remaining reported cases.
The overall median patient age was 6 years, with 31% being children aged 1-4 years, 27% being school-age children aged 5-17 years, and 29% were adults aged at least 18 years. However, when excluding the New York City (NYC) and New York state outbreaks, the median patient age was 19 years. Outbreak length also differed significantly between the NYC and New York state outbreaks, compared with all other outbreaks; the NYC outbreak lasted for 9.5 months, involving 702 patients from start to finish, the New York state outbreak lasted for 10.5 months and involved 412 cases.
The rate of patients who were either unvaccinated or had unknown vaccination status was similar in the New York outbreaks and in the other U.S. outbreaks, ranging from 87% to 91%. A total of 119 patients were hospitalized, 20% of whom were younger than 1 year; no deaths were reported. A total of 81 cases were internationally imported; the rate of patients who were unvaccinated or had unknown status in this group was 90%.
While most outbreaks in 2019 were similar to those previously seen, the outbreaks in NYC and New York state were more sustained for three reasons, the CDC investigators said: pockets of low vaccination coverage and variable vaccine acceptance, relatively high population density and closed social nature of the community, and repeated importations of measles cases among unvaccinated persons traveling internationally and returning to or visiting the affected communities.
“Public health authorities need to identify pockets of undervaccinated persons to prevent these outbreaks, which require substantial resources to control. A preventive strategy to build vaccine confidence is important, especially one that uses culturally appropriate communication strategies to offset misinformation and disseminate accurate information about the safety and importance of vaccination in advance of outbreaks,” the CDC investigators concluded.
The CDC investigators reported that they had no conflicts of interest.
SOURCE: Patel M et al. MMWR Morb Mortal Wkly Rep. 2019 Oct 4. .