Long COVID has variable incidence and clinical presentations: our 6-country collaborative study.

Following the acute COVID-19 disease, many countries see long-time sequences of this infectious disease, commonly known as Long COVID. This seems to be a multi-organ inflammatory chronic condition of variable intensity and incidence, partly due to the retention of the virus or viral particles in several organs. Based on our 6-country (4 in Europe, 2 from North America) collaborative investigations, we found that the incidence of Long COVID varied from 46 (Mexico) to 17% (Ukraine), the average being 25%. In a summary evaluation of all 6 countries, we characterized as "general" the most frequent presenting signs and symptoms: fatigue (47%), hair loss (39.2%), and myalgia (35%), but no two countries demonstrated the same top 3 clinical signs/symptoms. Hence, we promote the following 3 key points: 1. to expand international collaborations to better understand not only the prevalence and incidence of Long COVID but also to gain insights into the pathogenesis, and identify predisposing factors and diagnostic biomarkers of Long COVID; 2. find or develop new drugs for the treatments of Long COVID and identify appropriate rehabilitation, potentially organ-specific strategies; 3. most importantly, to start long-term observational studies (e.g., for 5-10-15 years) to identify potential increased cancer incidence in any organ, especially, since we know that certain viruses are carcinogens.