A large-scale review of the use of vaccines against five serious diseases has explored evidence related to their potential effects beyond protective benefits.
The results support the possibility of some additional effects other than those intended. The authors do not recommend any immediate changes in vaccination policy, but they do urge further studies to clarify whether such alterations might be advisable.
Following a recommendation from the World Health Organization, the international team of researchers, led by Julian Higgins of Bristol University in the UK, reviewed published data on the use of the BCG vaccine against tuberculosis; the DTP vaccine against diphtheria, tetanus and pertussis; and the measles vaccine. The data came from 68 research papers reporting observations of 34 cohorts of children in 15 countries in Africa, Asia, North America and the Caribbean. The studies compared children given one of the three vaccines against children who were not.
A key conclusion was that the BCG and measles vaccines might reduce overall mortality in young children by more than would be expected from their protective immunization effects alone.
The DTP vaccine, however, may be associated with an increase in mortality once the protective effect on the targeted diseases is discounted. This finding has led some academics and medics to question the wisdom of current DTP vaccination procedures.
Co-author Arthur Reingold of the University of California, Berkeley, emphasizes that the studies included in the review were observational rather than more rigorous, randomized, double-blind, placebo-controlled trials. He suggests that such studies are difficult to interpret because there was no prior control over which children received the vaccine and which did not. He suggests that differences in factors such as nutritional status and living conditions could generate spurious findings.
“It is plausible that much or all of the observed effects of DTP vaccination are attributable to such factors,” says Reingold. He adds that the current immunization schedule prevents large numbers of illnesses and deaths from the targeted diseases. Overall, Reingold concludes that “making changes to the current infant and childhood immunization schedule with the DTP vaccine is unwise at this time.”
Professor Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center and Harvard Medical School, says the paper is a review of multiple prior studies of varying quality, different populations, and conflicting results. "The findings associated with DTP vaccination in this study are not convincing," he says.