Kinetics of Delayed‐Type Hypersensitivity to Tuberculin Induced by Bacille Calmette‐Guérin Vaccination in Northern Malawi

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Abstract
During 1986–1989, a bacille Calmette-Guérin (BCG) vaccine trial was carried out in northern Malawi. The effects of age, sex, and prevaccination delayed-type hypersensitivity (DTH) on the time course of the DTH response over 1–36 months after vaccination were studied in 2418 persons. DTH response increased rapidly, to peak at 31–90 days after vaccination, when most persons had a measurable response. This was followed by a marked decline by 181–365 days, particularly in those <15 years old at vaccination, followed by a more gradual decline. Prevaccination DTH was the single best predictor of postvaccination DTH. BCG-induced DTH responsiveness appears to decline more rapidly in tropical than in temperate environments. This may reflect high prevalence of exposure to other infections, which induce a Th2 bias or compete for “space” within the T lymphocyte compartment. The inability of some persons to mount a persistent DTH response probably reflects genetic background and/or environmental exposure history

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