The heterologous (non-specific) effects of vaccines: implications for policy in high-mortality countries

There are important interactions between vaccines, and between vaccines and unrelated (heterologous) infections. In high-mortality regions, until the next vaccine is given, live vaccines such as bacillus Calmette-Guérin (BCG) and measles vaccines reduce mortality from infections such as pneumonia and sepsis. However, non-live vaccines such as diphtheria, tetanus and whole-cell pertussis vaccine (DTP) may increase mortality from infections other than diphtheria, tetanus and pertussis. All-cause mortality might be reduced if an extra dose of Edmonston-Zagreb measles vaccine were given at 20 weeks of age, 4-6 weeks after the third dose of DTP, with no subsequent doses of DTP in girls, and no vitamin A in girls or boys before the second dose of measles vaccine at 9 months of age. Policy should change to increase the proportion of babies given BCG and oral polio vaccine at birth, and should recognize the important differences between BCG, DTP and measles vaccines produced by different manufacturers.