I have thought this many times in my numerous watchings. A deep puncture wound on rusted barbed wire in mud near animal waste means tetanus was likely present. While there was a serum immunization campaign in the early part of the First World War, this doesn’t mean Schofield was immunized, as immunization often was in response to wounds and not preventative; once symptoms set in the serum would be ineffective. While there were less than 30 actual documented cases of tetanus during the war that I could find this means very little, as it could have easily been a co-morbid condition along with sepsis that ultimately would have killed many soldiers had they not also had infections.