A woman in China has tested positive for coronavirus six month months after recovering from the infection, according to local officials.
The 68-year-old, from Jingzhou city, which neighbours Wuhan, the epicentre of the pandemic, was diagnosed with Covid-19 for the second time on August 9.
She had tested positive previously on February 8 and beat the disease later that month, according to the Jingzhou government.
The patient has been quarantined and is receiving treatment. Her close contacts have all been tracked down and tested for the infection.
It comes a month after a doctor in Israel was diagnosed with Covid-19 for the second time and raises questions about our understanding of immunity against the disease.
So far, there have been no scientifically proven cases of someone catching it twice, with experts tending to blame inaccurate test results or lengthy illness. Some say it is not uncommon for parts of viruses to keep circulating even after recovery.
Traditional understanding of viruses suggests that people who have had Covid-19 already should develop a level of immunity that is at least temporary.
But cases such as this one call the idea of natural protection into question. As well as concerns about reinfection, there are also signs that people may simply remain ill for a long time with the virus still circulating in their bodies.
The case is one of a number that appear to show people getting diagnosed with the coronavirus more than once.
A scientific paper entitled ‘A case report of possible novel coronavirus 2019 reinfection’ was published in the US recently describing the case of an 82-year-old man who was hospitalised twice by the virus.
The unidentified man went to an emergency department at Massachusetts General Hospital after suffering from a high fever for a week.
He tested positive for Covid-19 and then his condition rapidly worsened while he was in hospital.
Doctors managed to save his life with a lengthy stay on a ventilator but he fell sick again less than a fortnight later, despite testing negative twice before being discharged.
He again needed intensive care and recovered for a second time, although the state of his health afterwards was not revealed.
Medics discussed in the The American Journal of Emergency Medicine how it was possible that the man recovered and tested negative but fell ill again.
His medics said that, rather than getting infected twice, it’s likely he never fully recovered the first time and that tests weren’t sensitive enough to notice he was still carrying the virus.
The doctors, led by Dr Nicole Duggan, said: ‘Many viruses demonstrate prolonged presence of genetic material in a host even after clearance of the live virus and symptomatic resolution.
‘Thus, detection of genetic material by [swab test] alone does not necessarily correlate with the active infection or infectivity.
‘Observational data suggest SARS-CoV-2 viral shedding may last 20-22 days after symptom onset on average with some outlying cases exhibiting shedding as long as 44 days.’
They said that in one 71-year-old woman, a study had found she continued to test positive for Covid-19 five weeks after her symptoms disappeared.
Because the virus was only first discovered in December, scientists have not had the opportunity to work out how it affects people in the long-term.
In one study done by the University of Amsterdam, researchers suggested the coronavirus may act in the same way as other coronaviruses that cause common colds and other infections.
The researchers followed 10 volunteers for 35 years and tested them every month for four seasonal and weaker coronaviruses named NL63, 229E, OC43, and HKU1.
Those viruses are much more common and cause mild illnesses similar to the common cold.
They found those who had been infected with the strains — from the same family as SARS-CoV-2, the type that causes Covid-19 — had ‘an alarmingly short duration of protective immunity’.
Levels of antibodies, substances stored by the immune system to allow the body to fight off invaders in the future, dropped by 50 per cent after half a year and vanished completely after four years.
By studying how people recover from viruses from the same family as the one that causes Covid-19, the scientists say their research is the most comprehensive look at how immunity might work for the disease that emerged in China last year.
Writing in the study, which has not yet been published in a scientific journal or reviewed by other scientists, the scientists said: ‘The seasonal coronaviruses are the most representative virus group from which to conclude general coronavirus characteristics, particularly common denominators like dynamics of immunity and susceptibility to reinfection.
‘In conclusion, seasonal human coronaviruses have little in common, apart from causing common cold.
‘Still, they all seem to induce a short-lasting immunity with rapid loss of antibodies. This may well be a general denominator for human coronaviruses.’