Detection of H1 Swine Influenza A Virus Antibodies in Human Serum Samples by Age Group1, Elien, Vandoorn, Isabel Leroux-Roels, Geert Leroux-Roels, Parys Anna, Amy Vincent, and Van Reeth Kristien , Emerging Infectious Diseases, Jan-09-2020, Volume 26, Issue 9, (2020)