COVID-19: What Happens After Recovery And Testing Positive –- WHO

* WHO said people who have recovered from COVID-19 don’t get infected again
* Patients who test positive again are expelling ‘left over material’ from their lungs
* South Korea already reported around 350 cases of supposed ‘reinfections’

People who test positive for coronavirus after already having been infected are not getting reinfected, according to the World Health Organisation (WHO).

Coronavirus patients declared recovered who later test positive are still expelling dead lung cells rather than getting a new infection, the organisation told AFP.

South Korean health authorities raised fresh coronavirus concerns after reporting more than 300 cases of recovered patients who later tested positive again.

If those who survive COVID-19 could become reinfected with the virus, it could complicate efforts to lift quarantine restrictions and produce a vaccine.

But such test results appear to be ‘false positives’ caused by lingering, but likely not infectious, lung cells and left over material.

An expert in virology told MailOnline that once the virus is inactivated by the immune system and forms a complex bond with an antibody, it stops being infectious but can still be detected by a swab test.

‘We are aware that some patients test positive after they clinically recover,’ a WH spokesperson told AFP, without making specific reference to the South Korean cases.

‘From what we currently know – and this is based on very recent data – it seems they these patients are expelling left over materials from their lungs, as part of the recovery phase.’

For some viruses, such as the measles, those who contract it are immune for life, while for other coronaviruses such as SARS, immunity lasted from a few months to a couple of years.

People infected with SARS-CoV-2 – the virus that causes COVID-19 – build up antibodies starting a week or so after infection or the onset of symptoms, research has shown.

But it is still not clear whether the body builds up enough immunity to ward off a new attack by the virus or, if it does, how long such immunity lasts.

‘We need systematic collection of samples from recovered patients to better understand how long they shed live virus,’ the WHO spokesperson said.

‘We also need to understand if this means they can pass the virus to other people – having live virus does not necessarily mean it can be passed to another person.’

WHO also said more research is needed on the recovered patients who originally tested negative and then tested positive weeks later.

In a recent interview with BBC, infectious disease epidemiologist Maria Van Kerhove, part of the WHO’s Health Emergencies Program, explained the ‘dead cell’ scenario.

‘As the lungs heal, there are parts of the lung that are dead cells that are coming up,’ she said, talking on The Andrew Marr Show on Sunday.

‘These are fragments of the lungs that are actually testing positive.

‘It is not infectious virus, it’s not reinfection, it’s not reactivation – it is actually part of the healing process that is being captured again as being positive.

‘Does that mean they have immunity? Does that mean they have a strong protection against reinfection? We don’t know the answer to that yet.’

South Korea had reported more than 350 cases of ‘reinfections’ as of Wednesday, according to the Korea Centers for Disease Control and Prevention (KCDC).

The country uses reverse transcription polymerase chain reaction (RT-PCR) tests, which detect the coronavirus’s genetic material.

The RT-PCR process can quickly return results and is considered the most accurate way to find out if a patient is infected with the coronavirus.

Ian Jones, Professor of Virology at the University of Reading, told MailOnline that once the virus binds with an antibody, it cannot infect any more.

‘However viral genome, the material that is tested by the RT-PCR test, can still be present and can be detected.

‘It is probably the reason there have also been reports of virus in blood, semen and faeces.

‘In all cases it is likely to the expelled inactivated virus rather than infectious virus.’

South Korean authorities are still gathering evidence to support their theory that the particles are from ‘dead’ virus cells, KCDC director Jeong Eun-kyeong said.

The patients were retested after they either exhibited new respiratory symptoms, or were selected for retesting by authorities.

Less than half of those retested by mid-April were showing symptoms, according to the KCDC, but authorities now say it is unlikely that those symptoms were being caused by the virus.

Patients who tested positive for the new coronavirus after recovering from COVID-19 do not appear to be infectious.

When investigating people who appear to suffer a relapse of symptoms after recovering from COVID-19, the KCDC takes cultures of the virus, a process that takes more than two weeks before reliable results become evident.

All 29 completed culture tests as of Wednesday had come back negative, although at least 79 are being processed.

‘The virus in the relapse cases have little to no infectiousness,’ Jeong said.

The KCDC has also not found a single case of patients who tested positive for the new coronavirus after recovering from COVID-19 passing the virus to another person, Jeong said.

In some cases, the RT-PCR tests may detect old particles of the virus, which may no longer pose a significant threat to the patient or others, said Seol Dai-wu, an expert in vaccine development at Seoul’s Chung-Ang University.

‘The RT-PCR machine itself cannot distinguish an infectious viral particle versus a non-infectious virus particle, as the test simply detects any viral component,’ Seol said, as quoted by Reuters.

Unlike hepatitis B or human immunodeficiency viruses (HIV), coronavirus does not infiltrate into the host cell’s nucleus, according to Oh Myoung-don, a doctor at Seoul National University Hospital.

That means it does not cause chronic infection and chances of it reactivating are very low, he said last week.

Authorities are also conducting tests to detect the presence of any antibodies that may have developed to fight the virus, and are testing and monitoring people who came into contact with the patients.

The pandemic has now killed more than 257,000 people globally and officially infected nearly 3.7 million.

Jonathan Chadwick, for Mailonline and AFP