COVID-19, caused by an infection with the SARS-CoV-2 virus, was declared a global pandemic by the World Health Organisation (WHO) in March 2020. While some people developed severe illness and required medical care, many people reported only mild-to-moderate symptoms, if any at all. However, many of the infected individuals have experienced persisting symptoms or frequent other infections months after the initial infection even if they weren-t much impacted by the disease to begin with.