Vaccines have sex differential non-targeted heterologous effects: a new dawn in vaccine research

The WHO Strategic Advisory Group of Experts (SAGE) on immunization recently published their conclusions from a systematic review of the ‘non-specific’ or ‘heterologous effects’ of vaccines, hailing a new era in our understanding of what vaccines do to the immune system. The report recognizes that bacille Calmette-Guérin (BCG) vaccine and measles vaccine (MV) may provide survival benefits against infectious diseases other than those targeted by the vaccine. These non-specific or heterologous effects of vaccines, whereby vaccines alter susceptibility to infections other than that targeted by the vaccine, can be beneficial as is the case for BCG and MV; but other vaccines such as diphtheria-tetanus-pertussis (DTP) vaccine may increase susceptibilty to infections, although WHO conclude that the data supporting deleterious effects of DTP are inconclusive.1 As a rule females seem to be more susceptible to these vaccine-induced heterologous effects than males.