Coronavirus: Doctors say reinfection is unlikely but many questions remain

Medics are trying to understand why some people test positive days or weeks after supposedly recovering from Covid-19

An elderly man,, wearing a face mask, walks past a closed restaurant in Madrid, during the hours allowed by the government to exercise, for the first time since the beginning of a national lockdown to prevent the spread of the Covid-19 disease. AFP

An anti lockdown protester is detained by police officers in London, following the outbreak of the coronavirus disease, London, Britain. Reuters

A young boy from a migrant workers' family waves from a railway compartment before the departure of a special train to Agra in Uttar Pradesh state during a government-imposed nationwide lockdown as a preventive measure against the coronavirus, at Sabarmati Railway Station on the outskirts of Ahmedabad. AFP

Thailand's Queen Suthida as she sews a face mask that will be donated to the public as a preventive measure against the spread of the coronavirus in Bangkok. AFP

People sit maintaining social distancing as Frontier Corps (FC) personnel distribute food on a street during a government-imposed nationwide lockdown as a preventive measure against the coronavirus, in Quetta. AFP

People visit the Empty Sky Memorial as the The One World Trade Center in New York is seen from Liberty State Park after many New Jersey Parks set to re-open during the outbreak of the coronavirus disease in Jersey City, New Jersey. Reuters

An Imam wearing a face mask wait for the start of the awareness campaign and distribution of sanitary products to people of extreme vulnerability by the REVOCAP association, amid the spread of the coronavirus disease, in Liberte 6 Baraka district of Dakar, Senegal. Reuters

Benjamin Hassan, a German ATP player wears a face mask as he warms up for an exhibition tennis match played without spectators and broadcasted by remote controlled cameras, during the spread of the coronavirus disease in a tennis academy in Hoehr-Grenzhausen, near Koblenz, Germany. Reuters

A young girl reacts as a Kenyan ministry of health medical worker takes a swab during mass tasting in an effort to fight against the spread of the coronavirus disease in the Kawangware neighbourhood of Nairobi, Kenya. Reuters

A Vietnamese volunteer prepares packages of food and protective masks for Vietnamese people in need and living in Japan, amid the coronavirus disease, at Nisshinkutsu temple in Tokyo, Japan. Reuters

A man walks through smoke generated by Nairobi municipality worker in an effort to fight against the spread of the coronavirus disease in the Kawangware neighborhood of Nairobi, Kenya. Reuters

A staff member of the Ministry of Health takes samples from a boy during the first day of mass testing of the coronavirus in Djibouti. AFP

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.

“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.