With reports of the first human death from bird flu in the US, some Americans are feeling an uncomfortable flashback to the early days of Covid-19, when infectious disease experts were talking about a new virus that was sending people to the hospital with respiratory infections.

The death comes at a time when the H5N1 virus has recently undergone an unusual mutation that is causing concern to the World Health Organization.

Those most likely to get infected are usually people who are in close contact with birds, such as poultry workers. The strains that can impact humans include A (H5N1) or A (H7N9), with H5N1 responsible for the first bird flu death in the US. Bird flu symptoms tend to appear three to five days after you’ve been exposed and infected by the virus.