A systematic two-sample and bidirectional MR process highlights a unidirectional genetic causal effect of allergic diseases on COVID-19 infection/severity

We performed a two-sample, bidirectional Mendelian randomization study for five types of allergic diseases with COVID-19 infection/severity (critically ill, hospitalized, and infection cases), and also further elucidated the potential underlying molecular mechanisms.Our MR analyses consistently suggest a unidirectional protective causal effect of asthma on COVID-19 infection/severity, but the reverse is not true.Food allergies such as shrimp allergy showed significant causal correlations with the risk of COVID-19 phenotypes.Allergic diseases may be causally correlated with COVID-19 infection/severity by inducing abnormal fluctuations of multiple immune-related cells and hematological traits in peripheral blood.The findings call for more attention to clinical monitoring of hematological traits and may be beneficial in developing effective therapeutic strategies for allergic patients following infection with COVID-19.