Evaluation of vaccines to prevent childhood pneumonia: Lessons relevant toplanning tuberculosis vaccine trials

Bacterial pneumonia in children is usually caused by one of the two leading pathogens, Streptococcus pneumoniae (pneumococcus) and Haemophilus influen za either type b (Hib) or nonencapsulated types. Hib conjugate vaccines sui table for use in infants have been available for about a decade, and experi ence with a trial of one of these vaccines in Africa showed that the vaccin es can prevent Hib pneumonia, as well as other manifestations of Hib diseas e. It also showed that vaccine trials can provide useful estimates of the r ole of Hib in childhood pneumonia, Trials of pneumococcal conjugate vaccine s that are currently under way have been designed to estimate disease burde n and efficacy. A major risk of vaccine trials that use bacteriologic end p oints is that the vaccine may affect the diagnostic test itself, creating a misleading impression of efficacy. Trials of future tuberculosis vaccines are discussed in light of these experiences. It is important that the trial s are designed to measure the effect on all clinical disease, as well as st rict microbiological end points. The existence of bacille Calmette-Guerin ( BCG) complicates future trials, and such trials should take into account po ssible nonspecific effects of BCG in addition to its effect on tuberculosis .