Introduction Flaviviruses, such as Zika virus (ZIKV), are primarily transmitted by infected arthropods. Evidence indicates that some of these viruses can be transmitted between persons through sexual intercourse. Sexual transmission of ZIKV is of special interest because of the risk of congenital abnormalities such as microcephaly. Several health agencies have produced guidelines on the prevention of sexual transmission of ZIKV, but there are many uncertainties. A systematic approach to assessment of the risk and epidemic potential of sexual transmission of flaviviruses is therefore crucial.

Methods We conducted a systematic review with questions derived from a conceptual framework of the key parameters that drive infection transmission. We searched multiple databases and websites for studies of any design and in any language. Because of the rapid increase in publications, we have developed the review as a living systematic review, allowing continual updating of the findings.

Results By January 10th 2017, we identified 28 unique reported cases of likely sexual transmission of ZIKV in 9 countries; 20 male to female, three female to male, one male to male, four unknown. In the US, 1% (36/4,310) of reported travel-associated ZIKV cases likely resulted from sexual contact. ZIKV has been detected by PCR for up to 188 days in semen and 14 days in vaginal secretions. Two of three included modelling studies quantified the contribution of the sexual transmission route, two studies estimated the proportion of ZIKV cases due to sexual transmission: 0.03 (95% CI: 0.001–0.46) and 0.23 (0.01–0.47). One publication about possible sexual transmission of West Nile virus has been identified so far.

Conclusion Sexual transmission of ZIKV can occur but is likely not sufficient to sustain an epidemic. In high risk groups with frequent sexual partner change, it might contribute more to secondary transmission. We are tracking this fast-moving research field in a living systematic review to fill gaps in the evidence about the risks and prevention of sexual transmission of flaviviruses.