Mumps

=== Clinical age and immunity ===
Mumps is found worldwide.<ref name="davison" /> In the absence of vaccination against mumps there are between 100 and 1,000 cases per 100,000 people each year, i.e. 0.1% to 1.0% of the population are infected each year. The number of cases peaks every 2–5 years,<ref name="who" /> with incidence highest in children 5–9 years old.<ref name="shu" /> According to seroconversion surveys done prior to the start of mumps vaccination, a sharp increase in mumps antibody levels at age 2–3 was observed.

Furthermore, 50% of 4–6 year olds, 90% of 14–15 year olds, and 95% of adults had tested positive to prior exposure to mumps, indicating that nearly all people are eventually infected in unvaccinated populations.<ref name="su" /><ref name="rubin" />

Prior to the start of vaccination, mumps accounted for ten percent of meningitis cases and about a third of encephalitis cases.<ref name="cdc" /> Worldwide, mumps is the most common cause of inflammation of the salivary glands.<ref name="kessler" /> In children, mumps is the most common cause of [[deafness]] in one ear in cases when the inner ear is damaged.<ref name="rubin" /> Asymptomatic infections are more common in adults,<ref name="who" /> and the rate of asymptomatic infections is very high, up to two-thirds, in vaccinated populations. Mumps vaccination has the effect of increasing the average age of the infected in vaccinated populations that have not previously experienced a mumps outbreak.<ref name="beleni" /> While infection rates appear to be the same in males and females, males appear to experience symptoms and complications, including neurological involvement, at a higher rate than females.<ref name="su" /><ref name="junghanss" />{{Primary source inline|date=November 2021}} Symptoms are more severe in adolescents and adults than in children.<ref name="senanayake" />