BOSTON - Temporary loss of smell is one of the earliest and most commonly reported COVID-19 symptoms.Although studies reported that it is a better indicator of the novel coronavirus than other common symptoms, such as a high fever and cough, scientists were still unsure about why the disease caused the loss of smell.Now, an international team of researchers at Harvard Medical School are beginning to understand the reason.In a study published in the peer-reviewed journal Science Advances, the researchers identified the olfactory cell types in the upper nasal cavity that are most vulnerable to SARS-CoV-2, the virus that leads to COVID-19.To their surprise, the researchers discovered that the sensory neurons that detect and transmit the sense.