Sex-disaggregated effectiveness data reporting in COVID-19 vaccine research: a systematic review

Plain Language SummaryThe level of protection that vaccines provide against COVID-19 might depend on a person's sex or gender. However, sex and gender are not always reported in studies on the effectiveness of COVID-19 vaccines. Here, we systematically reviewed the literature on COVID-19 vaccine effectiveness and looked at whether the studies we found separated out their data on vaccine effectiveness by participants' sex. Out of the 240 publications we identified, 68 (28.3%) did not report the sex of the participants in their study, and only 21 studies (8.8%) reported vaccine effectiveness data separated by sex. These results show that a substantial proportion of COVID-19 vaccine research publications do not account for sex. Efforts should be made by researchers to study and report the relationship between sex and vaccine effectiveness, to help to optimise vaccination strategies so that all people are adequately protected. BackgroundSex and gender are believed to influence vaccine response. Yet, the relationship between sex and gender and COVID-19 vaccine efficacy is poorly understood and remains under-investigated.MethodsWe conducted a systematic review to determine whether and to what extent post-approval COVID-19 vaccine effectiveness (VE) studies report sex-disaggregated VE data.We searched four publication and pre-publication databases and additional grey literature sources for relevant published/preprint studies released between 1 January 2020 and 1 October 2021 (i.e., pre-Omicron era). We included observational studies providing VE estimates for one or more licensed/approved COVID-19 vaccines and including both males and females. Two reviewers independently assessed study eligibility, extracted data, and assessed risk-of-bias through a modified version of Cochrane's ROBINS-I tool. A qualitative data synthesis was performed.ResultsHere we show that, among 240 eligible publications, 68 (28.3%) do not report the sex distribution among participants. Only 21/240 (8.8%) studies provide sex-disaggregated VE estimates, and high between-study heterogeneity regarding design, target population, outcomes, and vaccine type/timing prevent the assessment of sex in determining COVID-19 VE across studies.ConclusionsOur findings indicate that few COVID-19 vaccine research publications account for sex. Improved adherence to recommended reporting guidelines will ensure that the evidence generated can be used to better understand the relationship between sex and gender and VE. Sulis et al. perform a systematic review to investigate to what extent post-approval COVID-19 vaccine effectiveness studies report sex-disaggregated data. They identified 240 relevant publications, of which only a small percentage (8.8%) provided sex-disaggregated effectiveness estimates.