I had some covid hairless. Got sick with flu like symptoms that lasted about 2 weeks, and lost about half my hair. It grew back after a few months, thicker than before, and with some sort of slight wave in what was once perfectly strait hair. It is not just covid that will do this. Enough stress on the body will do this. All sorts of lasting sickness can do this. Poor diet, and weight gain can even stress the body enough to cause hair thinning and loss. Taking the stress away will typical result in restoration of the thinned hair.