Researchers have proved that a Hong Kong man was infected with coronavirus for a second time, according to a study published on Monday from the University of Hong Kong.The man, a 33-year-old IT worker, was released from hospital in April after being cleared of COVID-19. He tested positive for the virus again after returning from Spain at the beginning of August, rthk.hk reported. “Many believe that recovered COVID-19 patients have immunity against re-infection because most developed a serum neutralizing antibody response. However, there is evidence that some patients have waning antibody level after a few months," the researchers told rthk.hk. “Our findings suggest that the SARS-CoV-2 may persist in the global human population as is the case for other common cold-associated human coronaviruses, even if patients have acquired immunity via natural infection,” they said. "Since the immunity can be short-lasting after natural infection, vaccination should also be considered for those with one episode of infection," they added. The researchers emphasized that patients who recently recovered from COVID-19 should also wear masks and maintain social distancing.