Scientists are working to discover all they can about the behaviours of the COVID-19 coronavirus, from how it manifests itself in the body to how it spreads between people.
In treating those infected, patients are kept under strict quarantine for a period of time and are generally released after testing negative several times for the illness.
But a statement from a local government in Japan has said it recently recorded the first case of a person who has tested positive after apparently recovering from an earlier bout.
According to NHK, the woman, in her 40s, is a tour bus guide who travelled with tourists from Wuhan, China, in January.
She tested positive for COVID-19 on January 29 and was given the all-clear by February 6.
Just weeks later, the woman began exhibiting symptoms and was tested again - only for it to return as another positive result.
This has prompted reports about the possibility of people being "re-infected" with COVID-19 even though they could have fought off the virus a first time round.
But how realistic is the idea of re-infection? Here, Euronews asks the experts.
Was she re-infected?
Experts have stressed that nothing is really impossible while research is ongoing to find out everything there is to know about the virus.
But in terms of getting infected twice, they generally say other scenarios are more probable.
Connor Bamford, a virologist at the Wellcome-Wolfson Institute for Experimental Medicine at Queen's University in Belfast, told Euronews it is "unlikely" the woman was re-infected but underlined there was still a lot to learn.
He said: "This is potentially an important development but there’s still a lot we don’t know.
"Also, this is likely to be a rare event so it might not make much of an impact during the outbreak."
Meanwhile, Fabienne Krauer, an epidemiologist in Oslo, Norway, said: "We cannot know if this is a re-infection unless we explicitly know that the woman cleared the virus in between."
She went on to say that if it were the case as stated in Japanese reports that two tests in a month had returned positive, then "we can't tell if this is a real re-infection or a persistent infection."
Is it a persistent infection?
Short answer: it could be.
Philip Tierno, a professor of microbiology and pathology at NYU School of Medicine, told Euronews one possibility could be that the woman was "originally colonised" by the SARS-like illness - meaning it lingered in her body without her being "truly infected".
He said she may then have experienced "a very mild upper respiratory course, which did not evoke her immune system" and later tested negative if the test did not pick up the virus somewhere in her body.
"Later, she developed a significantly lower respiratory infection," he added.
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Put more simply, according to Bart Haagmans, a virologist at the Erasmus Medical Centre in Rotterdam, a mild initial infection could result in a limited response from the immune system.
This could allow the coronavirus to "replicate upon a second exposure," he said.
Any other possibilities?
Both Tierno and Bamford noted that it could just simply be a mistake made with the testing procedure.
"Tests are not perfect," Tierno said.
But, according to Bamford, these concerns about re-infection are not yet a priority.
He said: "We should keep an eye on this but I don’t think it is anything to worry about now.
"The vast, vast majority of cases are from first infections and these are the ones we should worry about."