“…Since the mutation rate of the influenza virus is rather high, vaccine efficacies are rarely 100%, and are more typically 30 -60%, against influenza-like illness. As significant as the estimated worldwide mortality is, it rises by another factor of 160% [4] to 260% [5] if influenza-induced complications to patients with other conditions are included, and the influenza vaccine on average significantly reduces such excess mortality [6]. Vaccine efficacy can even be negative, however, due to original antigenic sin [7][8][9], the tendency for antibodies produced in response to exposure to influenza vaccine antigens to suppress the creation of new, different antibodies in response to exposure to new versions of the influenza virus.…”