NEW DELHI : The first documented instance of coronavirus reinfection came from Hong Kong this week followed quickly by Belgium and the Netherlands reporting one case each, but there is no reason for alarm yet, say scientists, calming fears that a surge might be inevitable.As concerns mount that herd immunity may not be enough to curb the COVID-19 pandemic, scientists in India and elsewhere said more studies are needed for a reliable inference.Wide conclusions cannot be drawn about reinfection from individual cases, noted Belgian virologist Marc Van Ranst told PTI on the three cases reported this week. "Since we do not yet know how frequent reinfections are, it is difficult to say what these findings mean for the success of a vaccination.