Despite isolated reports of coronavirus patients making a recovery only to test positive again days later, scientists in South Korea say it is unlikely people can catch Covid-19 twice.
But they say reactivation may be taking place in people who thought they were free from infection.
Last week, doctors at the National Medical Centre in Seoul said it could take up to two weeks for the virus to die after infecting repository cells.
Pieces of its genetic material may remain in cells and be detectable in tests up to two months after infection, underscoring the limitations of such screening, doctors said.
This explains why some Covid-19 patients continued to test positive for more than a month, said Peter Collignon, a professor of clinical medicine at the Australian National University Medical School in Canberra, who advises the Australian government on infection control.
It’s possible the virus detected in these patients isn’t viable or capable of causing an infection, “but we need better animal models to see if it’s dead or alive", he said.
“The finding from South Korea fits in with most of the current thinking, but there are still a lot of unanswered questions about the duration of infectiousness,” said Mr Collignon.
How long a person excretes infectious virus in their respiratory secretions and faecal matter is key to determining the optimal time an infected person should self-isolate or be quarantined.
Previous studies indicated very ill patients typically remained infectious longer than people who experienced only mild symptoms.
This month, the Korean Centres for Disease Control and Prevention said the virus may have reactivated in people cured of Covis-19.
At the time, the agency found at least 51 patients classed as being cured had tested positive again. It concluded that, rather than being reinfected, the virus may have been reactivated in these people.
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“There have been more than 200 reconfirmed cases and there were discussions on how to explain them,” Oh Myoung-don, a professor of internal medicine at Seoul National University, said at a briefing last Wednesday.
“I can tell you the possibility of being reinfected after recovery is low.”
The issue of reactivation and reinfection has been difficult to pin down in part due to the unreliability of testing, with results showing positive cases one day and negative the next.
Fears of reinfection in recovered patients has also grown in China, where the virus first appeared in December.
There are reports some people tested positive again and some even died as a result of the virus after supposedly recovering and leaving hospital.
Epidemiologists across the world are trying to find out more about the virus that causes Covid-19.
In addition to research on possible reinfections, health experts are also focusing on patients who contract the virus but display few or atypical symptoms.
South Korea has been at the forefront of tracking these cases and the issue has raised particular concern in China, as the country tries to prevent a second wave of infections.r
South Korea was one of the earliest countries to experience a large-scale outbreak, but it has been one of the most effective in controlling the spread of the virus.
One of the world’s most expansive testing programmes and a tech-driven approach to tracing infections has allowed authorities in South Korea to contain the virus without imposing lockdowns or closing businesses.
