Sialic acids linked to glycoproteins and gangliosides are used by a broad range of viruses as receptors and/or attachment factors for cell entry [10]. These viruses include major human pathogens affecting the respiratory tract, such as influenza [21] and coronaviruses [22,23]. The attachment to sialic-acid-containing cell surface structures is mediated by receptor-binding proteins that belong to the viral spike. In the case of coronaviruses, this function is fulfilled by the S glycoprotein [9,24]. SARS-CoV and SARS-CoV-2 interact with the ACE-2 protein, which has been identified as a key determinant of the contagiousness of viruses [8]. However, considering the increased transmissibility of SARS-CoV-2 compared with SARS-CoV, binding to ACE-2 alone might not be enough to ensure robust infection of the upper respiratory tract. Thus, it is likely that SARS-CoV-2 might also bind to other cell surface attachment factors, such as sialic-acid-containing glycoproteins and gangliosides. Consistent with this notion, it has been shown that depletion of cell surface sialic acids by neuraminidase treatment inhibited MERS-CoV entry of human airway cells [25]. These data, which provide direct evidence that sialic acids play a critical role in human coronavirus attachment, broaden the therapeutic options to block the replication of SARS-CoV-2 that is responsible for the COVID-19 pandemic.