Shorter incubation period in symptomatic measles patients who had no history of measles vaccination.

In February 2024, a 22-year-old Japanese resident of Osaka Prefecture was diagnosed with measles in the PCR test. He had flown from Dubai to Osaka Kansai International Airport. We finally detected 13 incident measles cases identified as infected by the index case and collected data on these individuals to evaluate the association between vaccination and incubation period. The mean incubation period in all 13 infectees was 11.7 days (range: 7-20 days). The incubation period among infectees who had no history of measles vaccination ranged from 7 to 10 days (mean: 8.4 days), whereas it was significantly longer in those who had received any measles vaccine (p = 0.005). Moreover, the number of measles vaccinations received correlated positively with the length of the incubation period (p = 0.004).