Epidemiological survey of rubella immunity in Iran.

HUMAN PRE-EXPOSURE RABIES IMMUNIZATION 563 the 35 volunteers retested at 90 days the positive titres had persisted. The results of a first booster 1 year or more after the first dose of vaccine are limited to observations made on 23 volunteers (Table 2). The very high antibody titres obtained following these booster doses are particularly striking. Discussion The schedules of human prophylactic immuniza- tion currently recommended are based on obtaining a secondary immune response by spacing the inter- vals between inoculations, but this study has shown that three 2-ml doses of SMBV within 5 days pro- duced antibody levels as high as those reported in other studies using other vaccines and a longer im- munization schedule. REFERENCES Anderson, G. R., Schnurrenberger, P. R., Masterson, R. A., & Wentworth, F. H. (1960) Amer. J. Hyg., 71, 158-167 Atanasiu, P. (1966) Quantitative assay and potency test of antirabies serum. In: Laboratory techniques in rabies, Geneva, pp. 167-172, (World Health Organization Monograph Series, No. 23) Dieterich, W. H., Shelton, D. F., & Jenevein, E. P., Jr (1961) J. Amer. vet. med. Ass., 139, 99-1004 Fox, J. P., Koprowski, H., Convell, D. P., Black, J., & Gelfand, H. M. (1957) Bull. Wld Hith Org., 17, 869-904 Fuenzalida, E. & Palacios, R. (1955) Bol. Inst. bact. Chile, 8, 3-10 Godoy, A. M. de (1967) Arch. Fsc. Vet. (Minas Gerais), 19, 121-128 Habel, K. (1966) Habel test for potency. In: Laboratory techniques in rabies, Geneva, pp. 140-143 (World Health Organization Monograph Series, No. 23) Koprowski, H., Black, J., & Nelsen, D. J. (1954) J. Immu- nol., 72, 94-106 Peck, P. F., Powell, H. M., & Culbertson, C., G. (1955) J. Lab. clin. Med., 45, 679-683 Schnurrenberger, P. R., Anderson, G. R., Russell, J. H., & Wentworth, F. H. (1961) Amer. J. Hyg., 74, 1-6 Schnurrenberger, P. R., Anderson, G. R., & Russell, J. H. (1967) Bull. Wld Hlth Org., 37, 547-551 Tierkel, E. S. & Sikes, R. K. (1967) J. Amer. med. Ass., 201, 911-914 WHO Expert Committee on Rabies (1966) Wld Hlth techn. Org. Rep. Ser. No. 321 Epidemiological survey of rubella immunity in Iran S. SAIDI 1 Previous epidemiological studies in different parts of the world have demonstrated antibody to rubella in about 50% of children aged 6-8 years and in more than 80% of women of childbearing age. The antibody rates were significantly lower in the island, isolated, and rural populations investigated (Rawls et al., 1967; Dowdle et al., 1970). This survey was carried out to determine the age incidence of rubella in females and the immune status of the women of childbearing age in urban and rural areas of Iran. Materials and methods Sera. A total of 1 559 blood specimens were col- lected by venepuncture or by finger prick according 1 Associate Professor, Department of Epidemiology and Pathobiology, School of Public Health, University of Tehe- ran. Iran. to the method described by Chin et al. (1966); 731 sera were from school-age girls or from girls aged between 8 months and 15 years attending clinics or health centres in Teheran. From women of child- bearing age attending clinics and health centres and from high-school and college girls, 508 sera were obtained in Teheran, a city of about 3 million in- habitants, and 320 sera were collected in rural areas in the north and northwest of Iran. The age of these women ranged from 16 to 45 years. Sera were stored at -20°C prior to examination. Parallel titration of rubella haemagglutination-inhibition antibodies in several paired samples of blood obtained by vene- puncture and by finger prick gave similar results with a variation in titre of no more than twofold, the venous samples giving the higher titre. Haemagglutination-inhibition (HI) test. HI tests were carried out according to the method described 2831E BRIEF COMMUNICATIONS/NOTES Table 1. Age distribution of rubella Hi antibodies in female subjects Age group (years) No. positive/ % positive e 1 11/38 29 2-3 20/57 35 4-5 77/120 64 6-7 169/226 75 8-9 96/106 90 10-11 88/94 94 12-15 87/90 97 16-24 438/466 94 25-45 335/362 92 Total 1321/1559 85 by Halonen et al. (1967) using the microtitre tech- nique. Appropriate controls were included in each test run. Rubella haemagglutinating antigens and the reference sera were kindly supplied by the Wellcome Research Laboratories. Results The age distribution of rubella immune status in 1 559 females is summarized in Table 1. The overall immunity was 85 %, and the proportion of immune persons increased with age from 29% at 1 year of age to 97% at 15 years. Table 2 shows the frequency of rubella HI antibodies in women of childbearing age from rural and urban areas; 93% of the women were seropositive to rubella, and the proportion was significantly lower in rural areas (89%) than in the urban area (96 %). The HI titres ranged from 1: 10 to 1:1280. Geometric mean HI titre reciprocals among the immune persons did not significantly change with locality, and was about 165 for those from the urban area and 138 for those from rural areas. As is shown in Table 3, in the urban area the immune rate in women of low socioeconomic group was significantly higher (99 %) than in those of high socioeconomic group (92 %). Discussion From the results of this serological survey, it is. evident that the incidence of rubella is quite high in Iran, and therefore congenital rubella should be rare in the country. In the urban area, about 60% of the seropositive females were children under 5 years of age, the percentage reached 90% by the age of 9 years, and only 3% of the children were sero- negative to rubella after the age of 15 years. These data indicate that the age incidence of rubella in the urban areas of Iran is low, and that about 90% of the children are immune to rubella by the age of 9 years. The immune rates seem to be higher than those usually found in America, Europe and Asia. There was a correlation between the level of im- munity and population density. Of the women of childbearing age in the urban area, 96% had HI anti- body to rubella, whereas the percentage was sig- nificantly lower (89%) in rural and less populated areas (Table 2). In the urban area, immunity was significantly dif- ferent in women of different social class; of the Table 2. Distribution of rubella Hi antibodies in women of rural and urban areas Age group Urban Rural Total (years) No. positive/ % No. positive/ % No. positive/ % no. tested positive no. tested positive no. tested positive 16-24 344/359 96 94/107 88 438/466 94 25-45 143/149 96 192/213 90 335/362 92 16-45 487/508 96 a 286/320 89 b 773/828 93 a With geometric mean Hi titre reciprocals of 165. b With geometric mean HI titre reciprocals of 138. 564 RUBELLA IMMUNITY IN IRAN 565 Table 3. Immune status of women in Teheran by age and social class High socioeconomic Low socioeconomic Total Age group (years) No. positive/ % No. positive/ % No. positive/ % no. tested positive no. tested positive no. tested positive 16-24 148/161 92 196/198 99 344/359 96 25-45 50/55 91 93/94 99 143/149 96 16-45 198/216 92 289/292 99 487/508 96 women of high and low socioeconomic groups 92% and 99% respectively were seropositive to rubella (Table 3). There was no marked difference in rates between the two age groups studied by locality and social class. Since the proportion of rubella-susceptible women is low, mass vaccination is not necessary in Iran. However, periodic surveys for immunity are desirable, as well as diagnostic tests, with paired sera, of preg- nant women who have been in contact with a sus- pected case of rubella. ACKNOWLEDGEMENTS The author thanks Dr M. A. Faghih, Dean, and Dr K. Naficy, Head, Section of Viral Diseases, School of Public Health, University of Teheran, for their support and encouragement. Grateful thanks are due to Mrs G. Bahrami for technical assistance. This investigation was supported in part by funds from the Public Health Research Project of the Iranian Ministry of Health and Plan Organization. REFERENCES Chin, J., Schmidt, M. J., Lennette, H. E. & Hanahoe, M. (1966) Amer. J. Epidem., 84, 74-80 Dowdle, W. R. et al. (1970) Bull. Wld Hlth Org., 42, 419-422 Halonen, P. E., Ryan, J. M. & Stewart, J. A. (1967) Proc. Soc. exp. Biol. (N.Y.), 125, 162-167 Rawls, W. E. et al. (1967) Bull. Wld Hlth Org., 37, 79-88