Hong Kong scientists are reporting the case of a healthy man in his 30s who became reinfected with coronavirus four and a half months after his first bout.
They say genome sequencing shows the two strains of the virus are "clearly different", making it the world's first proven case of reinfection.
The World Health Organization warns it is important not to jump to conclusions based on the case of one patient.
And experts say reinfections may be rare and not necessarily serious.
There have been more than 23 million cases of coronavirus infection around the world.
Those infected develop an immune response as their bodies fight off the virus which helps to protect them against it returning.
The strongest immune response has been found in the most seriously ill patients.
But it is still not clear how strong this protection or immunity is - or how long it lasts.
And the World Health Organization said larger studies over time of people who had previously had coronavirus were needed to find out more.
This report, by the University of Hong Kong, due to be published in Clinical Infectious Diseases, says the man spent 14 days in the hospital before recovering from the virus but then, despite having no further symptoms, tested positive for the virus a second time, following a saliva test during airport screening.
"This is a very rare example of reinfection," said Brendan Wren, professor of microbial pathogenesis, at London School of Hygiene and Tropical Medicine.
"And it should not negate the global drive to develop Covid-19 vaccines.
"It is to be expected that the virus will naturally mutate over time."
Dr Jeffrey Barrett, senior scientific consultant for the Covid-19 genome project at the Wellcome Sanger Institute, said: "Given the number of global infections to date, seeing one case of reinfection is not that surprising even if it is a very rare occurrence.
"It may be that second infections, when they do occur, are not serious - though we don't know whether this person was infectious during their second episode."
Prof Paul Hunter, from the University of East Anglia, said more information about this and other cases of reinfection was needed "before we can really understand the implications".
Latest Stories
-
Two girls and one employee killed after explosion at Nebraska biofuels plant
2 minutes -
Analysis: Ghana’s gold exports surge in 2025, surpasses total imports for first time in a decade
11 minutes -
GH¢2bn was on the table, why collapse uniBank? – Prof Lord Mensah questions closure
13 minutes -
Mahama reiterates gov’t’s commitment to expand Damongo Water Supply system
20 minutes -
Bank of Ghana tightens rules on remittances amid compliance failures
26 minutes -
Gov’t releases $1m to avert Memphis University scholarship crisis
34 minutes -
President Mahama rallies African leaders to empower reparations bodies
43 minutes -
Parliament endorses use of oil and mineral revenues for ‘Big Push’ projects
56 minutes -
Prioritise funding to security agencies- Ntim Fordjour urges gov’t as he critiques Mid-Year Budget Review
58 minutes -
NPP leadership, Minority Caucus sign Daddy Lumba’s book of condolence
1 hour -
Defence Minister hails Ghana–China military ties at PLA anniversary event
1 hour -
Absa Black Star Marathon draws global participation and presidential endorsement
1 hour -
Gender Minister calls for review of Human Trafficking Act
1 hour -
Yagbonwura pays a historic visit to President Mahama
1 hour -
We’ve not apologised for GH¢138.9bn public debt overstatement – Audit Service
1 hour