Actually there might be a biological factor to it as well. Females have stronger innate and adaptive immune responses than males, which means faster clearance of pathogens and greater vaccine efficacy in females than in males. And there is a different process in the aging between males and females, many age-related diseases show sex-specific patterns, and although women live longer they are frailer and have worse health at the end of life. However to my knowledge, the data is not enough to draw any solid conclusion