Descriptive Analysis of Measles Transmission Among Travelers During Domestic and Inbound US International Air Travel, 2018‐2019

Measles is highly transmissible and can lead to severe complications and mortality risk. Cases of measles are reportable to the US Centers for Disease Control and Prevention (CDC). This study describes characteristics of travelers who flew while infectious with measles and their contacts. We analyzed data from domestic and US inbound international flights reported between January 1, 2018, and December 31, 2019. To identify contacts potentially exposed to measles during air travel we used the CDC-defined measles contact zone and crossmatched with the CDC measles database. We conducted a descriptive analysis of travelers with measles and their aircraft contacts and determined average time from flight exposure to contact interview. During the analysis period, CDC received reports of 83 air travelers infectious with measles resulting in 5,186 potential aircraft exposures. Health departments provided data to CDC for 39% (n=2,037) of the exposures/contacts. On average, 9.8 days elapsed between flight exposure and initial interview attempt. Of the 2,037 contacts interviewed, 82% (n=1,680) reported a history of vaccination or prior disease. Seven secondary cases were identified. Five were exposed on US inbound international flights, 5 had no history of vaccination, and 4 were seated outside the contact zone. Most contacts who developed measles were unvaccinated and shared a US inbound international flight with an infected traveler. Over half of secondary cases were outside the contact zone. The average first contact interview attempt occurred beyond the 3-day window for effective prophylaxis. Continued emphasis on measles vaccination, evaluation of the contact zone definition, and timely contact investigation of exposed travelers may prevent secondary cases and outbreaks in the United States.