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A senior expert of the World Health Organization (WHO) said on Thursday that although there are some cases suggesting that an individual may have been re-infected with COVID-19, it's still not confirmed.

Maria Van Kerkhove, technical lead on COVID-19 response at the WHO Health Emergencies Program, told a virtual press conference that some people can have PCR (polymerase chain reaction) positivity for many weeks, not just days, and it doesn't necessarily mean that they are infectious for that long.

According to the WHO expert, false positivity or false negativity may also lead to the result that an individual is tested positive again, but that should not be viewed as re-infection.

"What we ideally would like is to look at sequencing. If the virus can be isolated, if sequencing can be done, so we can look and see if somebody has been re-infected," she said.