Two patients in China who were cured of Covid-19 months ago tested positive for coronavirus again, raising concerns about the virus’ ability to prolong and recur in people who had previously been infected.
A 68-year-old woman in the central Chinese province of Hubei, where the coronavirus first appeared in December, tested positive on Sunday, six months after being diagnosed with Covid-19 and recovering. Another man who was found to have contracted the disease in April after returning from abroad tested positive in Shanghai on Monday but showed no symptoms.
None of the patients̵7; close contacts have tested positive for the virus, but they have been placed under quarantine, local authorities said.
Both cases are the latest addition to a growing number of “reactivation of the virus ”anecdotes found among patients believed to have recovered from the viral infection, which has infected more than 20 million worldwide and killed 748,000. While it is rare for recovered patients to test positive again, the phenomenon raises the question of why some patients suffer from long-term symptoms, and whether any immunity to the disease may be much more effective in protecting against re-infection.
Several studies have shown the level of protective antibodies that an infected person can build until fight the virus fast falls after only a few months, enabling them to be susceptible to the same pathogen a second time. However, there is little evidence so far that re-infection has been occurring in this pandemic.
Some experts have raised the possibility that others cells continue to impart immunity even after antibodies fade. Researchers in South Korea have suggested that the virus detected in patients months after recovery may be sucking dead virus particles that are no longer infectious.
– With the help of Sharon Chen, and Dong Lyu