22In late 2019, an outbreak of a severe respiratory disease caused by an emerging 23 coronavirus, SARS-CoV-2, resulted in high morbidity and mortality in infected humans 1 .
24Complete understanding of COVID-19, the multi-faceted disease caused by SARS-CoV-25 2, requires suitable small animal models, as does the development and evaluation of 26 vaccines and antivirals 2 . Because age-dependent differences of COVID-19 were identified 27 in humans 3 , we compared the course of SARS-CoV-2 infection in young and aged Syrian 28 hamsters. We show that virus replication in the upper and lower respiratory tract was 29 independent of the age of the animals. However, older hamsters exhibited more 30 pronounced and consistent weight loss. In situ hybridization in the lungs identified viral 31 RNA in bronchial epithelium, alveolar epithelial cells type I and II, and macrophages.
32Histopathology revealed clear age-dependent differences, with young hamsters launching 33 earlier and stronger immune cell influx than aged hamsters. The latter developed 34 conspicuous alveolar and perivascular edema, indicating vascular leakage. In contrast,
35we observed rapid lung recovery at day 14 after infection only in young hamsters. We
36propose that comparative assessment in young versus aged hamsters of SARS-CoV-2 37 vaccines and treatments may yield valuable information as this small-animal model 38 appears to mirror age-dependent differences in human patients.