evidence: For unknown causes of SID, attributable factors have been sought from various approaches. For instance, forensic autopsy cases of unexpected simultaneous twin deaths have been investigated extensively.4,5 Roberts6 demonstrated such a twin death, which occurred a couple of hours after diphtheria, tetanus and pertussis (DTP) vaccination, speculating that the immunization potentially gives a clue for the attributable factors. Another case report described twins found dead simultaneously after combined vaccine including DTP.7 Forensic autopsy has also revealed sudden death after DTP with mast cell increase as a relation to vaccination.8 By contrast, several large-scale studies have revealed that increased DTP immunization coverage is associated with decreased sudden infant mortality.9–14 Therefore, most SID syndrome (SIDS) cases are regarded as merely coincident, with no particular relation to DTP vaccination.15 [...] Google Scholar 11. Walker AM, Jick H, Perera DR, et al. Diphtheria-tetanus-pertussis immunization and sudden infant death syndrome. Am J Public Health. 1987;77:945–951. [...] Google Scholar 13. Müller-Nordhorn J, Hettler-Chen CM, Keil T, et al. Association between sudden infant death syndrome and diphtheria-tetanus-pertussis immunisation: an ecological study. BMC Pediatr. 2015;15:2–8.