Scientists reported the case of a healthy man in his 30s who became reinfected with coronavirus four and a half months after his first bout. There have been more than 23 million cases of coronavirus infection around the world. Those infected develop an immune response as their bodies fight off the virus which helps to protect them against it returning. The strongest immune response has been found in the most seriously ill patients. But it is still not clear how strong this protection or immunity is – or how long it lasts.