Epidemiology of measles in vaccinated people, Spain 2003-2014. / Epidemiología del sarampión en personas vacunadas, España 2003-2014.

INTRODUCTION: During the final phase of measles elimination rigorous investigation of each individual case becomes fundamental to confirm or discard cases, particularly among vaccinated people, since they experience a milder disease, and laboratory diagnosis is more complex. Our study focused in the epidemiology of measles in vaccinated people. METHODS: Longitudinal study on measles cases in two dose vaccinated people in Spain from 2003 to 2014. RESULTS: We confirmed 138 measles cases (90 of them, laboratory confirmed) in people with two doses of vaccine. The median of time from last vaccination to rash onset showed a lineal trend (P<.001), in parallel with the number of doses of vaccine received (0, 1, 2 doses). Among confirmed cases, the hospitalization risk decreased inversely proportional to the number of administered vaccine doses (linear trend, P<.001). Only in 23.9% of confirmed cases and 50% of discarded cases the guidelines about sample taking were fulfilled. 50% of samples in two dose vaccinated people were taken without fulfilling time delay criteria. 16.7% (36/215) of discarded cases with a negative IgM result did correspond to samples taken early (first 72h after rash) and could represent false negatives. CONCLUSION: Our results highlight the importance of fulfilling properly the guidelines for laboratory diagnosis in order to confirm or discard every measles case, especially in two dose vaccinated people. When a negative IgM result is obtained in early samples a new IgM test should be practiced, as well as a PCR test, in order to avoid infra-detection of cases.