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The aims of this paper were to estimate the numbers of tuberculosis notifications in young white adults which will be prevented in the next 25 years by the schools BCG vaccination scheme, and to assess the numbers of additional notifications if the scheme were to be discontinued. Assuming that in the white ethnic group in England and Wales the decline in tuberculosis notification rates (8-10% per year for ages less than 45 years) and efficacy of BCG vaccination (75-80%) are maintained, it is estimated that the scheme for BCG vaccination of schoolchildren with its present coverage will prevent 217 notifications in those aged 15-29 years in 1993, 119 in 1998, and 69 in 2003. The epidemiological consequences of stopping the BCG in schools scheme, whenever this occurs, would be a substantial slowing of the rate of decline of tuberculosis notifications, confined almost entirely to the 15-29 years age group, for a period of about 15 years, after which the steeper decline would resume. If the scheme stopped at the end of 1991 the annual number of additional notifications would slowly increase to a maximum of just over 80 about 15 years later, and then decrease. For stopping at the end of 1996 the maximum annual number of additional notifications would be about 50.

The effectiveness of BCG vaccination, at about age 13 years, in the prevention of tuberculosis at ages 15-24 years in England and Wales in 1983, has been determined by the same method as in two previous surveys in 1973 and 1978. In 1983, the tuberculosis notification rate among those vaccinated in the schools' scheme was 3.30 per 100,000, compared with an estimated rate of 13.20 per 100,000 among those who were tuberculin negative and not vaccinated in the scheme. The protective effectiveness of BCG vaccination at ages 15-24 years in England and Wales in 1983 is thus estimated as 75%; the estimated efficacy in the white ethnic group is closely similar, namely 76%. The estimated efficacy of BCG at ages 15-19 and 20-24 years in the three surveys, both in the white ethnic group and in the entire cohort, has been compared with that found in the Medical Research Council's controlled trial of tuberculosis vaccines which began in 1950. There is no evidence of any decrease in the protective efficacy of BCG vaccination between the four cohorts of young adults, which span a total period of 29 years. However, there were steep decreases between the cohorts in the annual notification rates for the white ethnic group; these decreases occurred in the BCG vaccinated and in the tuberculin negative unvaccinated groups, as well as among those found tuberculin positive (and not vaccinated) in the schools' scheme. It is concluded that the level of protective efficacy of BCG vaccination at ages 15-24 years is high, and has remained unchanged since the start of the BCG in schools' scheme. However, as the tuberculosis notification rate in young adults has decreased steeply throughout this period, and is continuing to decrease, the benefits to be expected from the BCG in schools' scheme will decrease equally rapidly.

Since the early 1960s notification rates for tuberculosis in England and Wales for the whole population have been influenced by high rates in certain ethnic groups. Using data based on country of birth from the British (Thoracic and) Tuberculosis Association surveys of 1965 and 1971, and based on ethnic origin from the Medical Research Council surveys in 1978/79 and 1983, rates for the white ethnic group have been estimated at those four times, and compared with the published rates for the whole population in 1953, when only a very small proportion was of non-white ethnic origin. Between 1953 and 1983 the notification rate for the white ethnic group fell from 122.2 to 11.3 per 100,000 for males, an annual decline of 7.7%, the corresponding rates for females being 90.1 and 5.8, an annual decline of 8.8%. The greatest annual declines occurred between 1953 and 1965, 9.4% for males and 11.2% for females. The annual declines in the most recent period, 1978/79 to 1983, were 6.9% for males and 7.3% for females. In both sexes the decline was greatest in the 15-24 year age group and least in the oldest age group, and this has led to a change in the age pattern of annual notification rates. The highest rates in both sexes occurred in young adults in 1953 but in the oldest age groups in 1983. There is however no evidence of any cohort experiencing an increase in notification rate with increasing age.

Study of a 10% sample of hospital admissions for asthma in England and Wales shows that in each age and sex group deaths have increased by at least a half between 1959 and 1964, while for males aged 15-44 years they have doubled. The number of deaths in hospital has risen in a similar way, and hence the hospital fatality rate has not changed over this period. Since study of certified absences from work has shown no comparable increase, it is suggested that the increase has occurred in the number of attacks of severe asthma requiring admission to hospital.