We report three simultaneous measles outbreaks with 112 confirmed cases in three Health Regions of Portugal, from February to April 2018. The mean age of cases was 30 years, 79% worked in a healthcare setting and 87% were vaccinated. Genotype B3 was identified in 84 cases from the three outbreaks. Primary cases in each outbreak were imported. Several cases presented with modified measles, highlighting the importance of rethinking the measles case definition for vaccinated cases.

Results: Over six months, 148 outbreak-related cases were reported: 87.8% occurred in three of the 16 affected counties and 78.4% had a known epidemiological link. Median age was 14.5 years (2-62) and 70.3% were 11-20 years old; 61.5% were male. The mean duration of disease was seven days (2-20). The disease was generally mild; 80.4% had fever and in 55.4% there was unilateral involvement of the parotid gland. Seven cases had orchitis, one oophoritis and one had nephritis. Two cases were hospitalized. School transmission predominated and class attack rates were < 30%. Most of the cases occurred in vaccinated individuals (92%) of whom 86.8% had received 2 doses; 17.7% had received one dose of the vaccine containing the Rubini strain. Mumps virus genotype G was identified in 4 cases. Discussion: This mumps outbreak among a highly vaccinated population, occurring mostly in teenagers at school, could be due to the partial effectiveness of the vaccine against the disease (particularly in the group vaccinated with Rubini strain), waning immunity overtime and genotype mismatch.Conclusions: This outbreak report shows the importance of discussion about the need of more booster dose of the actual vaccine or new vaccine including more genotypes to improve immunogenicity.

In Portugal, measles vaccination coverage and population immunity are high, and no endemic measles cases had been reported since 2004. The World Health Organization classified measles as eliminated in the country in 2015 and 2016, based on data from the previous 3 years. However, in a context of increasing incidence in several European countries in 2016 and 2017, Portugal experienced two simultaneous measles outbreaks with a total of 27 laboratory-confirmed cases (0.3 cases/100,000 population) in two health regions between February and May 2017. Nineteen cases (70.1%) were adults, of whom 12 were healthcare workers. Overall, 17 cases (63.0%) were not vaccinated, of whom five were infants younger than 12 months of age. One unvaccinated teenager died. Genotype B3 was identified in 14 cases from both regions. Measles virus sequencing identified different possible origins of the virus in each region affected. Although measles transmission was stopped in less than 2 months from the first case being notified, these outbreaks represent an opportunity to reinforce awareness of measles diagnosis. We highlight the intensity of the control measures taken and their impact on the rapid control of the outbreaks and also the fact that high vaccination coverage was crucial to stop transmission.

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