Severity of Measles among Patients with Incidental Postexposure Vaccination

It has not been well elucidated whether patients with measles who have undergone postexposure prophylaxis (PEP) exhibit milder clinical symptoms than would be expected in the absence of PEP. In the present study, we compared the severity of measles of patients who had undergone incidental PEP to those of patients who had not received such prophylaxis. An outbreak of measles occurred among the personnel of the Japan Self-Defense Forces (SDF) between 7 May and 14 June 2007 at 3 camps in or near Sendai City. All patients were admitted to SDF Sendai Hospital for isolation and care. Measles was confirmed in 21 patients (age: 21.9 ± 5.9 years). Of the 15 ill recruits (persons who had just joined SDF), 8 underwent incidental PEP on 10 May, 3 days after the onset of the prodromal symptoms in the first patient. The vaccination was not originally intended as PEP and was administered within the framework of a routine vaccination program. Compared to recruits without PEP (n = 7), the admission period was 5.6 days shorter, the period with high fever (39°C or more) was 2.7 days shorter, and the maximum body temperature was 1.1 °C lower in the recruits with PEP (n = 8). These results suggest that PEP ameliorates the clinical symptoms of measles.