Editorial: ‘Non‐specific effects of vaccines’– an important analytical insight, and call for a workshop

Abstract

keywords vaccines, mortality, analysis, bias, non-specificThis issue of the TMIH journal carries two papers by Aabyand his colleagues on the ‘non-specific effects’ of vaccines.They discuss a methodological issue that might explaininconsistent findings in papers published in recent yearswith respect to non-specific effects of DPT vaccination onchild mortality. In particular they point out that somecommonly applied methods of analysis may introducesubstantial bias in the estimation of such effects.It has long been known that vaccines can have effectsother than reducing the risk of the disease against whichthey are targeted. Perhaps most obvious are the adversereactions that, albeit rarely, can occur as a consequence ofvaccination – ranging from anaphylaxis attributable toparticular components (e.g. egg albumen) to pericarditisfrom smallpox vaccines. The pathogenesis of many of theseadverse effects is reasonably well understood, and warn-ings regarding the risk of such effects are described inpackage inserts of all vaccines. Less widely appreciated isthe fact that vaccines may have unanticipated beneficialeffects, other than on the target disease. For example, BCGvaccines, originally given for their protective effect againsttuberculosis, also protect against a variety of mycobacterialinfections (including Mycobacterium leprae and Myco-bacterium intracellulare). Beyond these examples is thepossibility that some vaccines may have less preciselydefined effects, perhaps mediated through the immunesystem, that manifest as a general increase, or decrease, inmorbidity or mortality attributable to a variety of causes ordiseases. It is with reference to such effects of vaccines thatthe term ‘non-specific’ is increasingly used.A striking example of an apparent non-specific effectwas described 15 years ago in the context of studiesevaluating the efficacy of high titre measles vaccines. Thesevaccines, carrying more than 10