The world’s patient zero, in China, began infecting others in the late fall of last year, the evidence thus far suggests. An analysis of the first 41 confirmed cases, all in people who had visited the same seafood market in Wuhan, indicates that the first hospital admission was on Dec. 16, 2019. The patient first noticed symptoms on Dec. 1, so the infection dates back earlier. Several scientists have estimated that the first outbreak began in late or mid-November, and have inferred a probable common viral ancestor, though additional virus samples could change the picture.
The level of detective work required to find the actual patient zero might be steeper than it appears. At least one genetic scientist has argued that the virus could have first infected humans — likely from a pangolin — well before last fall, in a form that did not cause sickness. It then evolved its pathogenic features over time, while circulating. If that’s the case, the question “Who came first?” may go without a conclusive answer for some time, perhaps for good.
How long you’ll be immune after infection.
Are people infected with the coronavirus protected from further infection? And, if yes, for how long?
The answers to these questions have broad implications for reopening the economy and allowing the public to live with less fear of infection in the short term — and for the effectiveness of vaccines in the long term.
Scientists have made steady, if incremental, progress in getting to the answers. When the body encounters any virus, it typically makes antibodies, some of which are powerful enough to neutralize the pathogen and prevent reinfection. It also produces large numbers of immune cells that can kill the virus.
Most tests that look for antibodies to the coronavirus have been flawed. But at least one team with a reliable test reported that most people, including those who were only mildly ill, make powerful antibodies. Data on immune cells has been slower to emerge, but a few studies suggest a robust response from immune cells as well.
What remains unknown is how long this immunity will last. There have been some reports of reinfection, but scientists have said that they are a result either of faulty testing, or of viral remnants that circulate long after the active infection has ended.