Cofactors that may influence vaccine responses

Purpose of review This review summarizes recent developments related to cofactors that may influence response to vaccination. Recent findings The unexpected increased HIV acquisition among vaccinees in the Step trial with prior exposure to adenovirus type 5 (Ad5) led to several studies trying to understand whether an underlying biological risk factor may have been responsible for this observation. Demographic factors and genetic background of the human populations in HIV vaccine trials remain a source of potential variation in responses observed in vaccine trials, yet empirical data remain limited on the impact of those factors. Coinfections, particularly those that may modulate the immune response, are a further concern for HIV vaccine trialists, with recent data providing further insight into effects of coinfections on innate and adaptive immunity and vaccine responses. Summary Individuals and human populations display variation in response to vaccination. Key explanatory variables for this variation include host factors, such as host genetics, and environmental factors, such as prior exposure to the vaccine vector, coinfection with other pathogens, and demographic factors. This review will outline some of the recent developments investigating the role of various cofactors on vaccine responses, with a particular emphasis on studies of HIV vaccines.