Sample size
decline in respiratory infections
ASYMPTOMATIC COVID-19, DISEASE
The total study will enroll ~1800 individuals. The proposed enrollment sample size is designed to provide 80% power to detect a 60% vaccine efficacy (a relative risk of 0.4 among the vaccinated). This is based on the observed threefold decline in respiratory infections in the South Africa adolescent cohort with 80% power and 0.05 type 1 error in a two-tailed test. We expect 5% of study participants to develop symptomatic COVID-19 during follow-up. We do not expect significant loss to follow-up among healthcare workers. We will plot Kaplan-Meier curves comparing COVID-19 disease between the BCG and placebo groups and report hazard ratios and 