Sex differences in outcomes of infections and vaccinations in under five-year-old children

Abstract

It is evident that human male and female children differ in their outcomes following infectious challenge and vaccination. This chapter explores some of the evidence for this in children <5 years of age, which is the age group that suffers the greatest morbidity and mortality from infections, and the target age group for many vaccinations. The sex-differential effects commence both preimplantation and in utero and continue throughout childhood. The mechanisms include genetic influences, epigenetic differences, the influences of sexually dimorphic hormones, sex differences in innate immunity, differences in thymic development, and sex differences in the effect of diet and breastfeeding. There may also be behavioral factors at play such as differential treatment of males and females. Studies in this age group are limited, and yet understanding the factors that determine key sex differences in immunity could lead to therapeutic strategies to improve childhood survival.