Covid—what do scientists now know about the virus and the disease it causes?

In early January, 2020, news began filtering through from China about a previously unknown illness, perhaps a new kind of pneumonia that appeared to have a high mortality rate. Our lives were about to be upturned, with lockdowns, border closures, masks and even toilet paper shortages transforming our day-to-day lives in unimaginable ways. Three years later, we know a lot more about Covid-19 and the virus that causes it, SARS-CoV-2.