Two European patients are confirmed to have been re-infected with COVID-19, raising concerns about people’s immunity to the coronavirus as the world struggles to tame the pandemic. The cases, in Belgium and the Netherlands, follow a report this week by researchers in Hong Kong about a man there who had contracted a different strain of the virus four and a half months after being declared recovered – the first such second infection to be documented. That has raised fears about the efficacy of potential vaccines against the virus, which has killed hundreds of thousands of people, though experts say there would need to be many more cases of re-infection for these to be justified. Belgian virologist Marc Van Ranst said the Belgian case was a woman who had contracted COVID-19 for the first time in March and then again with a different coronavirus strain in June. […]