Eight months of living with Covid-19 has taught us much about the world’s most disruptive coronavirus in a century. But while we know to wear a mask when leaving home, sanitise and wash hands thoroughly and keep a safe distance from others, there is much we still do not know. Hong Kong researchers have caused concern among some about the effectiveness of vaccines being developed with the first scientifically proven case of a person being reinfected with the disease. As alarming as that would seem, the World Health Organisation and others have soberly warned that it is wrong to jump to conclusions from the experience of a single patient and larger studies are needed. The 33-year-old man was confirmed with having Covid-19 on returning from a trip to Spain, 4 1/ 2 months after being first infected and recovering. Genome sequencing by scientists at the University of Hong Kong showed the two virus strains were different, confirming the reinfection. But that is not cause for panic as the case is a rarity among the more than 23 million global infections so far reported and the seriousness is uncertain. It does not mean the search for a vaccine and other treatments is in vain. Viruses mutate and scientists and health officials have to be ready to modify and change. As the pandemic has evolved, a diverse range of cases has emerged, with susceptibility and severity differing from place to place among age groups and communities, and pre-existing medical factors playing a crucial role. A Hong Kong mother and her 19-month-old son who recently tested positive for Covid-19 had antibodies in their blood and showed no symptoms, so were released from hospital as they were not considered at risk of transmission. Dutch and Belgian patients also got coronavirus a second time Those infected usually develop an immune response that helps them fight off the virus, which should protect them from it returning, although that is now obviously not the case for everyone. Research of individual cases improves understanding, but it is also essential to have the means to know where and how outbreaks occur. Some governments have perfected that ability, but have still been unable to stave off resurgences. Far greater in-depth study is necessary to prevent what we still do not know from causing harm.