Rotavirus A infections can occur throughout life: the first usually produces symptoms, but subsequent infections are typically mild or asymptomatic,[16][17] as the immune system provides some protection.[18]:106-124[19] Consequently, symptomatic infection rates are highest in children under two years of age and decrease progressively towards 45 years of age.[20] Infection in newborn children, although common, is often associated with mild or asymptomatic disease;[3] the most severe symptoms tend to occur in children six months to two years of age, the elderly, and those with compromised or absent immune system functions. Due to immunity acquired in childhood, most adults are not susceptible to rotavirus; gastroenteritis in adults usually has a cause other than rotavirus, but asymptomatic infections in adults may maintain the transmission of infection in the community.[21]