New Delhi: Putting the belief to rest that recovered covid-19 patients have immunity against re-infection because most developed a serum neutralizing antibody response, The University of Hong Kong (HKU) on Monday documented the world's first case of covid-19 re-infection.Researchers from Department of Microbiology, Li Ka Shing Faculty of Medicine, The University of Hong Kong (HKU), said that they have proven the first instance of human re-infection by SARS-CoV-2 by using the next generation sequencing.The team showed that the genome sequence of the virus strain in the first episode of covid-19 infection is clearly different from the genome sequence of the virus strain found during second episode of infection.The scientists have cautioned.