Research on subgroups is not research on equity attributes: Evidence from an overview of systematic reviews on vaccination

Background: Equity remains a priority in the international health development agenda. However, major inequities in vaccination coverage jeopardise the achievement of the Sustainable Development Goals. We aim at comprehensively describing how research has addressed equity issues related to vaccination. Methods: We carried out an overview of systematic reviews (SRs) that explicitly explored the effects of interventions to improve vaccination in any context; for any vaccine and, in any language. We followed standard research synthesis methods to systematically search for SR, assess them for inclusion and extracting relevant data, particularly on vaccination related outcomes. To gather evidence on equity issues addressed in the SR, we used the PROGRESS-plus framework. Findings: Our search obtained 2,003 hits which resulted in 54 included SRs, published between 1994 and 2014. The quality of SRs was generally poor, with less than half complying with most of the quality criteria. Reported vaccines included, by order of frequency, influenza and Expanded Programme on Immunisation vaccines. The types of interventions more frequently reported were related to vaccination delivery strategies, financial support and information, education and communication. Most of the SRs suggested effects favouring intervention groups as opposed to comparison groups. The most frequently reported equity attribute was 'place of residence' and the least reported equity attributes were sexual orientation and religion. Very few estimates of effects actually measured differences or changes between groups having those attributes and all of them referred to the place of residence. No data was found about reducing equity gaps for vulnerable groups or minorities, or attributes such as sexual orientation, education or specific religious groups. Conclusions: Although research on vulnerable populations as a subgroup is abundant, it fails to report on the interventions that will actually reduce inequities and consider how redistribution of health care resources could shrink the gap between the privileged and most vulnerable groups including minorities. Research, if aiming at being responsive to global health policy trends, needs to report not only on specific attributes but also on how a better redistribution of health care resources could contribute to alleviating the unjust situation of the most vulnerable populations.