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expert reaction to people being re-tested positive for coronavirus after initial recovery

There has been a case reported in Japan where a woman has been confirmed as a coronavirus case for 2nd time, after previously recovering from the illness.


Prof Mark Harris, Professor of Virology, University of Leeds, said:

“The reports that patients who tested negative subsequently tested positive again is clearly of concern.  It is unlikely that they would have been reinfected having cleared the virus, as they would most likely have mounted an immune response to the virus that would prevent such reinfection.  The other possibility therefore is that they did not in fact clear the infection but remained persistently infected.   Although coronaviruses generally cause short-term self-limiting infections which are cleared, there is some evidence in the scientific literature for persistent infections of animal coronaviruses (mainly in bats). Clearly we need more information about these patients, such as were there underlying medical conditions or a change in circumstances that might have allowed the virus to escape immune control? This highlights the need for more research into the biology of the new coronavirus, it is very much early days in our efforts to understand it.”


On case in Japan: Prof Paul Hunter, Professor in Medicine, University of East Anglia (UEA), said:

“Regarding this reported case:

 “There is so much we do not know about this case to give a properly informed opinion. Did the woman test negative after her last positive and if so how many tests were negative before her initial discharge? Does she have any underlying illness or is she on any treatment that could affect her immune system?

“So there are a two possibilities

  1. This is indeed a relapse of the illness – This was seen is SARS but in someone who was being treated with steroids. It is possible that the illness could be biphasic as suggested by Dr Tierno though this is unlikely to be common based on current information.
  2. She has a prolonged excretion of virus from her initial infection and tests were either not done or were not done sufficiently well or enough to confirm clearance. It does appear that swabs for the virus are not 100% reliable. In this case it is even possible that the recent sore throat maybe unrelated. COVID-19 tends to cause upper respiratory tract symptoms rather less frequently that did SARS.

“I would caution against reading too much into this report given the lack of information. However, the report reinforces the fact that we have to investigate all such findings really thoroughly and report such information if we are to make the best decisions based on sound scientific evidence. At this time I would council against changing management guidelines based on this case but we do need to always keep them under review.”


On case in Japan: Prof Rowland Kao, Sir Timothy O’Shea Professor of Veterinary Epidemiology and Data Science, University of Edinburgh, said:

“Assuming that there is a minimal possibility of misdiagnosis, it still remains unclear from the published reports whether the person involved was likely re-infected, or whether this represents an infection that may have been partially cleared or perhaps has gone latent. In either case, given the number of reported cases thus far, it would seem unlikely that this is a common occurrence, and thus should have only a small impact on the overall epidemic projections themselves. Of possibly greater concern are the implications for control measures – should quarantine periods be extended? It also makes contact tracing even more difficult, potentially straining resources.”


All our previous output on this subject can be seen at this weblink:


The SMC also produced a Factsheet on COVID-19 which is available here:


Declared interests

None received.

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