My family member was prescribed an antibiotic (Co-amoxiclav) while they had COVID-19, but I didn’t think antibiotics worked against a virus?
Co-amoxiclav is an antibiotic. Antibiotics do not treat any viruses including Coronavirus, but they are absolutely essential for treating bacterial infections. Patients with COVID-19 are very susceptible to secondary bacterial infections which can only be treated with antibiotics. It may be that your family member had developed a secondary bacterial infection.