Clinical age and immunity<unk>  is found worldwide. In the absence of vaccination against<unk>  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, with incidence highest in children 5–9 years old. According to seroconversion surveys done prior to the start of<unk>  vaccination, a sharp increase in<unk>  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<unk> , indicating that nearly all people are eventually infected in unvaccinated populations. Prior to the start of vaccination,<unk>  accounted for ten percent of meningitis cases and about a third of encephalitis cases. Worldwide,<unk>  is the most common cause of inflammation of the salivary glands. In children,<unk>  is the most common cause of deafness in one ear in cases when the inner ear is damaged. Asymptomatic infections are more common in adults, and the rate of asymptomatic infections is very high, up to two-thirds, in vaccinated populations.<unk>  vaccination has the effect of increasing the average age of the infected in vaccinated populations that have not previously experienced a<unk>  outbreak. 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. Symptoms are more severe in adolescents and adults than in children. Settings of outbreaks It is common for outbreaks of<unk>  to occur. These outbreaks typically occur in crowded spaces where the virus can spread from person to person easily, such as schools, military barracks, prisons, and sports clubs. Since the introduction of vaccines, the frequency of<unk>  has declined dramatically, as have complications caused by<unk> . The epidemiology in countries that vaccinate reflects the number doses administered, age at vaccination, and vaccination rates. If vaccine coverage is insufficient, then herd immunity may be unobtainable and the average age of infection will increase, leading to an increase in the prevalence of complications. Risk factors include age, exposure to a person with<unk> , compromised immunity, time of year, travel history, and vaccination status.<unk>  vaccination is less common in developing countries, which consequently have higher rates of<unk> . Cases peak in different seasons of the year in different regions. In temperate climates, cases peak in winter and spring, whereas in tropical regions no seasonality is observed. Additional research has shown that<unk>  increases in frequency as temperature and humidity increase. The seasonality of<unk>  is thought to be caused by several factors: fluctuation in the human immune response due to seasonal factors, such as changes in melatonin levels; behavior and lifestyle changes, such as school attendance and indoor crowding; and meteorological factors such as changes in temperature, brightness, wind, and humidity.
Mumps
Chickenpox
Smallpox
Larva currens
Cowpox
Sealpox
Scabies
Malaise