Both.
Obesity, and/or poor immune system.
Coronavirus is the common name for Coronaviridae and Orthocoronavirinae, also called Coronavirinae.
Coronaviruses cause diseases in mammals and birds. In humans, the viruses cause respiratory infections, including the common cold, which are typically mild, though rarer forms such as SARS (including the one causing COVID-19) and MERS can be lethal.
Symptoms vary in other species: in chickens, they cause an upper respiratory disease, while in cows and pigs coronaviruses cause diarrhea.
Other than for SARS-CoV-2, there are no vaccines or antiviral drugs to prevent or treat human coronavirus infections.