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BCG vaccination of children against leprosy in Uganda: final results
Insights
BCG vaccination significantly reduced leprosy incidence by 80% in Ugandan children over 8 years. This protection persisted for over a decade, highlighting BCG
Area of Science:
- Tropical Medicine
- Infectious Disease Epidemiology
- Vaccinology
Background:
- Leprosy remains a significant public health challenge, particularly in endemic regions.
- Contact tracing and preventative measures are crucial for controlling leprosy transmission.
- Bacille Calmette-Guérin (BCG) vaccine is known for its protective effects against tuberculosis and has been investigated for leprosy prevention.
Purpose of the Study:
- To evaluate the efficacy of BCG vaccination in preventing leprosy among child contacts of known leprosy patients.
- To assess the duration of BCG-induced protection against leprosy.
- To investigate the protective effect of naturally acquired tuberculin sensitivity.
Main Methods:
- A controlled trial involving 19,200 children in Uganda (1960-1964) who were contacts of leprosy patients.
- Random allocation of tuberculin-negative or weakly positive children to BCG vaccination or unvaccinated control groups.
- Long-term follow-up (average 8 years, extended to 13+ years) with standardized leprosy case ascertainment.
Main Results:
- BCG vaccination resulted in an 80% reduction in leprosy incidence compared to controls over 8 years.
- Protection was observed across different initial tuberculin statuses, sexes, and contact types.
- A 58% lower incidence of leprosy was noted in strongly tuberculin-positive children (naturally acquired sensitivity).
- Continued protection was evident up to 12-13 years post-vaccination.
Conclusions:
- BCG vaccination is highly effective in preventing leprosy among child contacts.
- The protective effect of BCG vaccination is substantial and long-lasting.
- Naturally acquired strong tuberculin sensitivity also confers significant protection against leprosy.
Abstract:
A total of 19 200 children, all contacts or relatives of known leprosy patients, and all free of visible leprosy lesions, were included in a controlled trial of BCG vaccination against leprosy in Uganda between 1960 and 1964. They were followed for an average of 8 years, during which time 261 developed early leprosy lesions. A less comprehensive follow-up was carried out for a further 5 years, when 8 more cases of leprosy were identified.In the main intake, between 1960 and 1962, 16 150 tuberculin-negative or weakly tuberculin-positive (Heaf Grades O-II) children were allocated by an effectively random process to either a BCG-vaccinated or an unvaccinated control group. Both groups were seen and examined in an identical fashion for leprosy at approximately 2-year intervals, and precautions were taken to ensure unbiased assessment of new cases of leprosy. After 8 years, 41 cases of leprosy had been identified in the BCG-vaccinated group, and 201 in the control group, a percentage reduction in the BCG-vaccinated group compared with the control group of 80%. The percentage reduction was similar for those initially tuberculin-negative, and for those initially weakly positive, and did not depend upon the age at vaccination. It was also similar for both sexes, for contacts of lepromatous and contacts of non-lepromatous leprosy, for children having contact with one or more than one patient, and for differing grades of physical contact and genetic relationship with a patient. The protective effect of BCG vaccination continued over the 8-year period, although it may have fallen off slightly at the end.In a group of 1074 strongly tuberculin-positive (Heaf Grades III-IV) children followed in parallel with the other two groups a total of 16 cases of leprosy were identified. When adjusted for age, this incidence is 58% lower than that in the unvaccinated control children who were initially tuberculin-negative, indicating a protective effect against leprosy of naturally-acquired strong tuberculin sensitivity.Between 1970 and 1975, one new case of leprosy was identified in a child who had initially been strongly tuberculin-positive and had therefore not been vaccinated, one in a BCG-vaccinated child, and 6 in control children. Although the follow-up in this period was less comprehensive than that in the main part of the trial, the ascertainment of cases was unlikely to have been biased towards either vaccinated or control children. These results indicate a continuing protective effect of BCG up to 12-13 years after vaccination.