The COVID-19 pandemic has highlighted the vulnerability of people with diabetes mellitus (DM) to respiratory viral infections. Despite the short history of COVID-19, various studies have shown that patients with DM are more likely to have increased hospitalization and mortality rates as compared to patients without. At present, the mechanisms underlying this susceptibility are unclear. . The reasons for this are likely multifactorial, including the presence of hyperglycaemia, glycaemic variability as well as selected medication use. Here, I present our most recent data showing the mechanisms by which type 2 diabetes mellitus impairs anti-viral immunity and increases disease severity.