There are reports of recovered COVID-19 patients being tested positive again in China, South Korea and Japan. However, solid scientific evidence is needed to address questions like: How accurate were the test results? Was the recovered patient reinfected with the virus, or did they have an infection that simply lasted a long time? Are there variations in immune response among different people? How many different versions of COVID-19 may be spreading around? These questions could help us understand the immune response of the virus.