Academic journal article Bulletin of the World Health Organization

Case-Control Evaluation of a School-Age BCG Vaccination Programme in Subtropical Australia

Academic journal article Bulletin of the World Health Organization

Case-Control Evaluation of a School-Age BCG Vaccination Programme in Subtropical Australia

Article excerpt

Introduction

A controlled trial of BCG vaccination of school-children in England that started in 1950 reported that the protection afforded was 59-78% over 15) year [1-3]. As a result, a BCG vaccination programme directed at children aged 12-14 years was instituted in Queensland schools in 1956, and within a few years was being carried out in all appropriate schools throughout the state. In Queensland the incidence of tuberculosis has been steadily falling over the last 20 years (Fig. 1), as it has in many developed countries, including the other Australian states, some of which, such as New South Wales, have had no population-wide BCG programme.

The Queensland State Health Department required information on the effectiveness of this school programme against tuberculosis in adults to enable it to consolidate the decision made in 1986 to discontinue the vaccination programme for those at a low risk of infection. This need was subsequently recognized by the National Health and Medical Research Council, which recommended investigating the efficacy and applicability of BCG vaccination also in other Australian states and territories. (a)

Aboriginal people and refugees or other immigrants from south-east Asia are two groups that are at greater risk of tuberculosis than the general Australian population. These groups are routinely afforded special screening, vaccination, and surveillance services against tuberculosis. In consequence, they were excluded from this study. The study was therefore carried out on the relatively low-risk general population in Queensland, who were aged 15-44 years in 1985, and who could have been vaccinated in the secondary school programme.

The vaccination procedure

During the early years of the programme, children in the age group concerned (12-14-year-olds) were in the final year of primary school; however, following a change in 1962, this age group became the first year of secondary school. Subsequently, all schools were visited annually--beforehand some remotely situated schools had been visited only once every 2 years. All children in the target age group were eligible, except for a small number in remote rural areas who received their education at home through the "school of the air" radio broadcasts.

At the vaccinator's first visit, an individual record card was prepared for each child attending, and all were tuberculin tested. Two days later, at the second visit the test was read and the result recorded on the card. If written parental agreement had been obtained, the negative reactors (Heaf grade 0) and a small proportion (about 10%) of the weak positive reactors (Heaf grade I) were BCG vaccinated. No subsequent examination was made to determine whether the vaccine had "taken", i.e., had produced a local lesion. Intermediate positive (Heaf grade II) and strong positive reactors (Heaf grades III and IV) were not vaccinated, but the latter were put under clinical surveillance for tuberculosis. The record cards were stored alphabetically in the regional tuberculosis control offices.

Methods

Epidemiological approach

A restrospective cohort study was considered intially on the basis of the existing school card system. After exclusion of high-risk population groups, the rates of tuberculosis notification in Queensland were, however, extremely low. A cohort design would therefore have required the processing of an impracticably large number of cards to ensure that enough cases were found to make credible estimates of the value of the programme. A case-control methodology, using the obligatory tuberculosis notifications to identify cases, was therefore chosen. Smith has pointed out the advantages of this method for developing countries and for the vaccination of newborn infants [4]. In such situations, BCG scars, and not vaccination records, are the more usual indicators of vaccination status. …

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