The sex disparity in COVID-19 mortality varies widely and is of uncertain origin. In their recent Nature paper “Sex differences in immune responses that underlie COVID-19 disease outcomes,” Takahashi et al. assess immune phenotype in a sample of COVID-19 patients and conclude that the “immune landscape in COVID-19 patients is considerably different between the sexes,” warranting different vaccine and therapeutic regimes for men and women -- a claim widely disseminated following the publication. Here, we argue that these inferences are not supported by their findings: this study does not demonstrate that biological sex explains COVID-19 outcomes among patients. This study is diagnostic of an ongoing pattern in sex difference research of overstatement of findings and superficial treatment of factors beyond innate sex in analyzing the causes of gender/sex disparities in health outcomes.