Covid-19: what we know and do not know about the coronavirus

Reports woman tested positive for a second time show there are still many unknowns

• Coronavirus - latest updates

Reports that a woman in Japan has tested positive for the Covid-19 disease for a second time, after seemingly recovering, will alarm scientists and public health experts trying to control the spreading epidemic, and underlines how much we still do not know.

There are a number of possible explanations for the second positive test of the woman, in her late 40s, a resident of Osaka who worked as a tourbus guide. She first tested positive for coronavirus in late January and was discharged from hospital on 1 February after recovering. She tested negative again on 6 February.