AbstractBackgroundWomen have been significantly more likely than men to express hesitancy toward COVID-19 vaccination and, to a lesser extent, to refuse vaccination altogether. This gender gap is puzzling because women have been more likely to perceive higher risks from COVID-19, to approve more restrictive measures to fight the pandemic and to be more compliant with such measures.MethodsThis article studies the gender gap in COVID-19 vaccination attitudes using two nationally representative surveys of public opinion fielded in February 2021 and May 2021 in 27 European countries. The data are analyzed using generalized additive models and multivariate logistic regression.ResultsThe data analyses show that hypotheses about (i) pregnancy, fertility and breastfeeding concerns, (ii) higher trust in Internet and social networks as sources of medical information, (iii) lower trust in health authorities and (iv) lower perceived risks of getting infected with COVID-19 cannot account for the gender gap in vaccine hesitancy. One explanation that receives support from the data is that women are more likely to believe that COVID-19 vaccines are unsafe and ineffective and this leads them to perceive the net benefits of vaccination as lower than the associated risks.ConclusionsThe gender gap in COVID-19 vaccine hesitancy results to a large extent from women perceiving higher risks than benefits of the vaccines. While accounting for this and other factors decreases the gap in vaccine hesitancy, it does not eliminate it completely, which suggests further research is needed.