Previous research from low-resource nations has raised concerns about the non-specific effects of whole-cell pertussis immunization, especially in females. The purpose of this study was to look at the impact of sex and birth weight on health-care usage after receiving the whole-cell pertussis vaccination for the first time. Researchers examined the relative incidence of emergency department visits and/or hospital admissions between sexes and birth weight quintiles using a self-controlled case series approach using relative incidence ratios (RIRs). Females showed a greater relative frequency of incidents following immunization than males, which maintained after birth weight adjustment. They also found a tendency of increased relative event incidence with decreasing birth weight quintiles; babies in the lowest quintile had a 26% higher relative event rate than those in the highest quintile, which was resistant to sex adjustment. 

Female babies and newborns with lower birth weights had a higher likelihood of using all-cause health care soon after immunization. More research is needed to establish whether or not vaccination dosage should be based on baby weight.