As the COVID‐19 pandemic continues to rise, the development of effective vaccines is of crucial importance to prevent further morbidity and mortality. In parallel, some rare adverse events related to COVID‐19 vaccines, have been reported, most of them mild. Here we report the case of a previously healthy 19‐year‐old woman who developed optic neuritis 1 week after single dose of Ad26.COV2.S vaccine with marked improvement after management with steroids. Although causality cannot be confirmed due to lack of a biological marker, this case may help to guide further research for potential pathogenic mechanism. [ABSTRACT FROM AUTHOR]