CD4 and hepatitis A virus infection: In Bangladeshi infants, the pre-vaccination presence of Bifidobacterium was positively associated with some adaptive immunological responses, such as CD4+ and CD8+ T-cell proliferative responses to BCG and tetanus toxoid vaccinations as well as specific IgG responses to tetanus toxoid and hepatitis B vaccines, whereas high levels of enteric pathogens such as Enterobacteriales and Pseudomonadales were associated with neutrophilia and poorer vaccine responses (55).