Worrisome headlines have appeared across Asia: some patients in China, Japan and South Korea who were diagnosed with COVID-19 and who appeared to be cured were readmitted to hospital after testing positive for the virus.
Because SARS-CoV-2, the new coronavirus that causes COVID-19, was only discovered a few months ago, scientists are still trying to answer many big questions about the virus and the disease it causes. . This includes knowing whether patients can be re-infected with the virus after they seem to be recovering from symptoms.
With other strains of coronaviruses, experts say the antibodies patients produce during infection give them immunity to the specific virus for months or even years, but researchers are still figuring out if and how this works with COVID-19.
The answer has huge implications for the spread of the disease, as researchers believe it will continue to crash across the world in waves, hitting the same country multiple times.
Can you be reinfected after recovering from COVID-19?
There is still a lot of uncertainty, but the experts TIME spoke of say it is likely that reports of patients who appeared to have recovered but then tested positive again were examples of reinfection, but were cases where a persistent infection was not detected by tests for a period of time.
Experts say the body’s antibody response, triggered by the appearance of a virus, means that patients who have recovered from COVID-19 are unlikely to be reinfected anytime soon after contracting the virus. Antibodies are normally produced in a patient’s body about seven to 10 days after the initial appearance of a virus, says Vineet Menachery, virologist at the University of Texas Medical Branch.
Instead, a positive test after recovery could simply mean that the tests resulted in a false negative and that the patient is still infected. “It may be because of the quality of the sample they took and perhaps because the test was not so sensitive,” said David Hui, an expert in respiratory medicine at the University. from Hong Kong who also studied the 2002-2003 epidemic of severe acute respiratory syndrome (SARS), which is caused by a coronavirus of the same family as SARS-CoV-2.
A positive test after recovery could also detect residual viral RNA that remained in the body, but not enough to cause the disease, Menachery says. “Viral RNA can last a long time, even after the virus has stopped.”
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Where have patients tested positive for COVID-19 after appearing to have recovered?
A study of COVID-19 patients recovered in the city of Shenzhen, in the south of China, revealed that 38 of the 262, or nearly 15% of the patients, were positive after their discharge. They have been confirmed by PCR (polymerase chain reaction) tests, currently the reference standard for coronavirus tests. The study has not yet been peer reviewed, but provides an early overview of the potential for reinfection. The 38 patients were mostly young (under 14 years of age) and had mild symptoms during their infection period. Patients were generally not symptomatic on their second positive test.
In Wuhan, China, where the pandemic started, researchers examined a case study of four medical workers who underwent three consecutive positive PCR tests after apparently recovering. Similar to the Shenzhen study, the patients were asymptomatic and their family members were not infected.
Outside of China, at least two of these cases have also been reported in Japan (including one Diamond princess cruise) and one case has been reported from South Korea. All three would have shown symptoms of infection after a first recovery, then re-tested as positive.
Does COVID-19 recovery make you immune?
There has not been enough time to research COVID-19 to determine if patients recovering from COVID-19 are immune to the disease – and if so, how long will immunity last. However, preliminary studies provide some clues. For example, a study by Chinese researchers (which has not yet been peer reviewed) found that antibodies in rhesus monkeys prevent primates that have recovered from COVID-19 from being infected again when exposed to the virus.
In the absence of more information, the researchers looked at what is known about other members of the coronavirus family. “We have only been in the pandemic for three and a half months,” said Hsu Li Yang, associate professor and expert in infectious diseases at the National University of Singapore. “The comments we make are based on previous knowledge of other human coronaviruses and SARS. But if they extrapolate through COVID-19, we are not so sure yet. “
A study by Taiwanese researchers found that survivors of the 2003 SARS epidemic had antibodies that lasted up to three years, suggesting immunity. Hui notes that survivors of the Middle East Respiratory Syndrome (MERS, which is also caused by a virus linked to the one that causes COVID-19) have been found to last about a year.
Menachery estimates COVID-19 antibodies will stay in a patient’s system for “two to three years”, based on what is known about other coronaviruses, but says it’s too early to be known certain. The level of immunity can also differ from person to person depending on the strength of the patient’s antibody response. Younger and healthier people are likely to generate a more robust antibody response, which will give them better protection against the virus in the future.
“We expect that if you have antibodies that neutralize the virus, you will have immunity,” said Menachery. “How long the antibodies last is still in question. “
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