Association between COVID-19 Primary Vaccination and Severe Disease Caused by SARS-CoV-2 Delta Variant among Hospitalized Patients: A Belgian Retrospective Cohort Study, Robalo, Queeny, De Mot Laurane, Vandromme Mathil, Van Goethem Nina, Gabrio Andrea, Chung Pui Yan Jenny, Meurisse Marjan, Catteau Lucy, Thijs Carel, and Blot Koen , Vaccines, Jan-01-2023, Volume 11, Issue 1, (2023)