Vaccines and mortality

It has been known for decades that routine childhood vaccines confer a survival benefit beyond preventing the disease against which they are targeted. This effect is most obvious in the poorest communities. The BMJ has published two related systematic reviews, commissioned by the WHO's Strategic Advisory Group of Experts (SAGE), to help decide if any changes are needed to internationally recommended vaccination schedules. The first looked specifically at mortality (Higgins J, et al. doi: http://dx.doi.org/10.1136/bmj.i5170). They found 34 studies, most from low-income countries. Overall, BCG was associated with reduced relative all-cause mortality risk of 0.70 (95% CI 0.5–1.0), and measles-containing vaccines with a similar risk reduction of 0.74 (95% CI 0.5–1.1). For both vaccines, the observed reduction was considerably greater in controlled trials as opposed to observational studies. However more surprisingly, they found an increased mortality risk associated with DTP vaccine (RR 1.38; 95% CI 0.9–2.1). All these DTP studies were observational. An accompanying commentary by Chee Fu Yung is at pains to point out that bias probably explains this result, for example the vaccine may not have been given to ‘frail’ children more at risk of dying anyway …