Cross-Neutralizing Activity Against SARS-CoV-2 Variants in COVID-19 Patients: Comparison of 4 Waves of the Pandemic in Japan. - Furukawa K; Tjan LH; Sutandhio S; Kurahashi Y; Iwata S; Tohma Y; Sano S; Nakamura S; Nishimura M; Arii J; Kiriu T; Yamamoto M; et al. (Open forum infectious diseases, 2021)