Vaccines are often less effective in very young children whose immune systems are immature. For the past 35 years, vaccines have been conjugatedcombined with a carrier protein a cross-reactive material (CRM)that enhances the immunogenicity of polysaccharide antigens.  [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4964734/] The carrier protein CRM197 (Product #149 [https://www.listlabs.com/products/buy-diphtheria-toxin-crm197,-mutant]), under consideration here, is a mutant version of Diphtheria toxin [https://www.listlabs.com/products/diphtheria-toxins/], in which the single amino acid exchange of a glycine in position 52 to a glutamic acid renders the protein non-toxic: it is one of the most widely used and highly effective carrier proteins  [https://www.ncbi.nlm.nih.gov/pubmed/26841683]. List Labs CRM197 has been used in a wide range of medical research, leading to a better understanding of the mechanism behind serious illnesses at all stages of the human life cycle. Most of the studies to date have employed animal models because direct research in humans would be ethically impossible.