Epidemiology

Before the vaccine’s introduction, mumps was a common childhood disease, with the highest number of cases in children aged 5-9 years.[2]​ A review of worldwide serosurveys to assess mumps immunity showed that 50% of children aged 4-6 years and 90% of children aged 14-15 years were seropositive, indicating that nearly all people in an unvaccinated population would become infected. In countries without vaccination against mumps virus, the incidence remains high, with epidemic peaks every 2-5 years.[3]

In Europe, the introduction of the MMR vaccine has led to a decrease in incidence of mumps; for example, Finland has eliminated mumps.[7] In the UK, the cases that do occur are generally in the older, unvaccinated population. In 2019, 5718 lab-confirmed cases of mumps infection were reported in England and Wales, the highest figures since 2009, with only 5% of patients under 15 years old and 75% aged 15-29 years.[8] Reported cases were lower in 2020 (3738 cases, with almost all in the first quarter) and in 2021 (provisional data report 18 confirmed cases), likely due to COVID restrictions.[8]

After the introduction of the mumps vaccine in 1967, the incidence of the disease declined initially by 99% in the US. Subsequently, outbreaks of mumps were reported between 1986 and 1987 in people born too early to receive the mandatory vaccine for school entry, leading to revised vaccine guidelines for young children and college-aged adolescents.[9]​ This was followed by historically low rates of mumps and a goal for its elimination by 2010.[10] However, in 2006, the US reported 6584 people with mumps (an increase from 314 cases in 2005).[11] Most of these cases were seen in the Midwest and occurred in people aged 18-24 years who were attending college. Additionally, most cases occurred in vaccinated individuals.[12] Since 2006, reported numbers have fluctuated, decreasing to 229 in 2012, and peaking again at over 6000 in 2016 and 2017.[11] In 2020, the number of reported cases decreased sharply compared with 2019 (reducing from 3780 to 616), possibly due to COVID-19 restrictions, with cases remaining low in 2021, 2022, and 2023 (154, 322, and 436, respectively).[11]

There is no difference in the prevalence of mumps between men and women. However, men are more likely to have complications, particularly neurological complications.[2]

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