This hexavalent vaccine combines five components diphtheria, tetanus, pertussis, polio and Haemophilus influenzae type b along with Merck's genetically engineered HepB vaccine, Recombivax. The latter contains a problematic proprietary aluminum adjuvant possibly linked to serious autoimmune conditions. 

A number of European studies have identified concerns about hexavalent vaccination and SIDS, in particular. In one Italian study, researchers found that in 12% of the cases, the SIDS deaths occurred within one to seven days of hexavalent vaccination. The authors deemed it plausible that "vaccine components could have a direct role in sparking off a lethal outcome in vulnerable babies."