Specific and non-specific effects of health interventions on child mortality in low-income countries: Public health implications of contrasting disease-health models

Vaccination policies in low-income countries assume that vaccines have specific effects by preventing targeted infections and do nothing else. In the disease-specific model, policy and overall impact assessment can be based on assessment of specific immune responses/clinical protection and disease-burden. Once the disease is eradicated it becomes cost-effective to stop vaccination. These assumptions were never tested.

An increasing number of observational studies and randomised trials indicate that all routine vaccinations have non-specific effects (NSE) on morbidity/mortality not explained by specific prevention. A review of evidence related to BCG, DTP, OPV and measles vaccine suggests these generalisations: First, NSEs are more important for survival than the specific effects. Second, live vaccines have beneficial effects whereas inactivated vaccines may have detrimental effects. Third, the most recent vaccination has the strongest effect on survival and combination and sequence of vaccinations are therefore important. Fourth, NSEs are often sex-differential. Firth, vaccines may interact with immune-enhancing interventions like micronutrients. Sixth, eradicating the disease and eliminating a live vaccine may cost more lives than those saved by eradication campaigns.