One of the symptoms which often appeared for COVID-19 was the loss of smell, although we did not know the reason behind it. An international team of researchers led by the Harvard Medical school may have found the explanation behind this occurrence. Published in the journal Science Advances, their findings identified the olfactory cells in the upper nasal tract that are vulnerable to the SARS-CoV-2 which causes COVID-19. 
However, it does not affect the neurons that find and transmit the sense of smell to the brain. Instead, it seems to attack the supporting cells. These are cells that provide structural and metabolic support to the olfactory sensory neurons. It can also attack some stem and blood vessel cells. The good news is that it means that the resultant loss of smell, or anosmia, is not long-term. Since it does not target the olfactory neural circuit, the anosmia is not permanent.
Sense of loss is a more persistent symptom among COVID-19 patients when compared when cough and cold. Clinical records show that patients are 27 times more likely to experience loss of smell, but only 2.2 to 2.6 more likely to experience cold and cough. These patients also regained their sense of smell with time.
For the latest updates on COVID-19, please visit the CDC and the NIH.