Non-specific effect of Bacille Calmette-Guérin vaccine on the immune response to routine immunisations.

Bacille Calmette-Guérin (BCG) is one of the most commonly administered vaccines worldwide. In addition to protection against tuberculosis (TB), evidence suggests that BCG immunisation has a number of additional beneficial non-specific immunological effects. These include a reduction in overall infant and child mortality attributable to causes other than TB in high-mortality regions. The antibody response to immunisations provides an opportunity to investigate the influence of BCG on the immune response to unrelated antigens. This study compared the antibody response to routine immunisations in BCG-immunised and non-BCG-immunised infants. BCG-immunised infants were recruited from a related study in which BCG was given at birth and non-BCG-immunised infants were recruited from immunisation clinics. All infants received their routine immunisations according to the Australian National Immunisation Program. Concentrations of antibodies against pneumococcal (anti-Pn Ps), Haemophilus influenzae type B (anti-Hib), tetanus toxoid (anti-TT) and hepatitis B surface (anti-HBs) antigen were measured four weeks after the last (six month) set of infant immunisations. A total of 127 parents agreed for their infants to take part in the study of which 108 were included in the final analysis (56 BCG-immunised and 52 non-BCG-immunised). The geometric mean concentration (GMC) of anti-Pn Ps IgG for all serotypes, anti-Hib IgG and anti-TT IgG were higher in the BCG-immunised group than the non-BCG-immunised group. This difference reached statistical significance for serotype 9V (p<0.01) and 18C (p=0.04). The GMC of anti-HBs IgG was lower in the BCG-immunised group than the non-BCG-immunised group (p=0.03). The majority of participants in both groups had antibody levels above the protective threshold. BCG immunisation at birth influences the antibody response to routine immunisations administered later in infancy. This has important implications for the introduction of both pneumococcal conjugate and novel TB vaccines in resource-limited countries.