The development of tissue culture techniques for the cultivation of rubella virus and for the detection of neutralizing antibody in patients with rubella [lo, 181, followed by the demonstration that rubella could be transmitted only to subjects who did not have neutralizing antibody, individuals with pre-existing antibody being immune [l, 2, 5, 6, 11, 12, 161, made it possible to determine the frequency of susceptibility to rubella in different populations.Sever et al. [15] found that 18 % of 600 women 1 P 4 4 years old from different parts of the United States did not have neutralizing antibody against rubella virus, a higher incidence of susceptibility demonstrated in the negro (21 yo) than in the white women (14 %). A sample from Honolulu, Hawaii, revealed 44 % without antibody. The frequency of antibody was not significantly associated with histories of rubella. Dudgeon et al. [3] found 9 seronegative specimens among 50 cord bloods (18 %) from a London obstetric hospital and 6 seronegative among 25 cord bloods (24 %) from Kampala, the This study was supported by the Swedish Medical Research Council (Project No. 19x-762-01) and by the County Council of Sodermanlend. capital of Uganda. Further studies by Sever et al. [13] showed that 60 % of 228 pregnant women in Hawaii had no antibody to rubella. Nagayama et al. [9] found 35 % seronegative among 193 serum specimens from pregnant women 18-40 years of age in Fukuoka city and its suburbs in Southern Japan.Givan et al.[4] studied small groups of females of different age in Toronto, Canada, and found neutralizing rubella antibody in about 10 % of children up to 4 years increasing to about 80 Yo in those 35-40 years old. These tests were performed with a serum dilution of 1 : 6. It was also reported that the incidence of females with higher antibody levels (a titre of a t least 24) reached a peak of more than 50 % in the age group 15-19 years falling to 20 % in those 35-40 years old. Sever et al. [14] determined the frequency of antibody in serum specimens from 268 individuals in Montgomery County, Maryland, U.S.A., collected in 1957. The frequency of serological immunity increased from approximately 35 yo in children 1-10 years of age to 85 % in the group 16 years and older.
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