July 18, 2021 The Moderna vaccination centre in Radin Mas Community Club. Studies show immunity wanes in recovered patients over time. SINGAPORE - Getting people who have recovered from Covid-19 to take at least one vaccine dose is a reasonable precaution, say infectious disease experts, given that not much is known about the strength of immunity from natural infection and how long this protection lasts. What scientists know for certain is that a small number of people have been infected twice, with studies showing immunity wanes in recovered patients over time. "In a way, we are regarding the actual infection as the first dose of a vaccine, therefore only one jab is needed," explained Professor Dale Fisher, a senior infectious disease consultant at the National University Hospital.