Epidemiological studies on rubella.

Serological surveys of rubella antibody were carried out using the hemagglutination-inhibition test, with a view to studying the distribution of seroimmune individuals according to age and intermingling with other populations. Specimens were collected from different age groups including infants, children and adults, among the inhabitants of Montreal from 1963 to 1968. From the results obtained it was possible to establish the pattern of rubella antibody development in this urban community. Surveys were also conducted among the inhabitants of Les Iles de la Madeleine, a Canadian island in the Gulf of St. Lawrence, and among the population of Easter Island, an isolated island in the South Pacific remote from any large land mass.It was seen that, among the inhabitants of Montreal, presumably maternally acquired rubella antibody was present in 95% or more of the infants, the same percentage of seroimmune individuals as was found among the adult women 25 to 30 years of age. Passively acquired rubella antibodies decreased rapidly, attaining their lowest levels among children 1 to 2 years old. Rubella infection occurred in young children and its incidence rose steeply from school age to adolescence, leaving 7 to 9% of the adults without antibody. The highest geometric mean antibody titres were found among children 4 to 10 years of age.The same pattern of rubella antibody development was found among the population of Les Iles de la Madeleine, except that in adults the percentages of seropositives reached practically 100%. Antibody titres decreased with advancing age and became lower than those found among children.Detection of rubella antibody in serum samples derived from the inhabitants of Easter Island indicated that this population had experienced rubella infection not long before the Canadian Medical Expedition of 1964-1965. This status is determined from the high proportion of seroimmune individuals in each age group and the uniformly high antibody titre.Island populations appear to represent the ideal subjects for estimating the duration of the immunity conferred by any attenuated rubella vaccine that will eventually be licensed.