Pneumococcal Vaccine Trials in Papua New Guinea: Relationships Between Epidemiology of Pneumococcal Infection and Efficacy of Vaccine

have shown that pneumococcal capsular polysaccharide vac-cine protects children <2 years of age from death due to acute lower respiratory infections (ALRI). The vaccine appears to reduce mortality by preventing bacteremia. Evidence suggests that highly invasive "adult " pneumococcal serotypes are comparatively more important as a cause of ALRI in developing countries where ALRI-related mortality is higher than in North America. Capsu-lar polysaccharide vaccines are more likely to be immunogenic for these serotypes than for the "pediatric " serotypes. The evaluation of pneumococcal vaccines in areas where mortality is high should have the highest priority. fur such trials investigators should, at minimum, define epidemi-ologic circumstances in terms of (1) the invasive serotypes of pneumococci, (2) the protective levels of antibody, (3) the antibody response to vaccination, and (4) the general immune status of the population. Trials of pneumococcal polysaccharide vaccine in Papua New Guinea have provided evidence that the vaccine protects children <2 years old from death due to acute lower respira-tory infections (ALRI) [1].This finding is in apparent conflict with the present understanding of the immunogenicity of the vaccine and with results from trials of pneumococcal vaccine for prevention of otitis media [2]. The most convincing evi-dence in favor of the vaccine was obtained from three trials of its use in young men living in institutions subject to epi-demic pneumococcal pneumonia [3-5]. The purposes of this paper are to explore the similarities between the epidemio-logic circumstances in these institutions and those among infants living in the highlands of Papua New Guinea and to argue that the epidemiology of disease must be taken into con-sideration when the efficacy of a vaccine is evaluated and new trials are designed. Trials of Vaccine in Healthy Young Adult