It's true that our cohort is all patients that were hospitalized for COVID-19, but notably, our long COVID questionnaire specifically asked which new symptoms they had after COVID-19 that they didn't already have beforehand. That, plus the direct link to acute patterns of gene expression and antibodies specific to SARS-CoV-2, makes a strong case for a causal link between acute SARS-CoV-2 infection and long COVID a year later. While we don't look at mild non-hospitalized cases in this study, there's no reason to think a causal link wouldn't exist there as well.