When you are infected with a virus, your immune system produces very specific antibodies to try and fight it off. It’s these antibodies that then provide us with immunity from future outbreaks of the same virus. If the virus comes back, the necessary antibodies are swiftly called to action and defeat it before it can make you feel unwell.
However, reports emerged in February of a lady in Japan who was apparently given the all-clear having developed COVID-19, but who then tested positive for the virus a second time. But the biggest question this scenario raises is in regards to the reliability of the tests.
The bottom line is we simply don’t yet know whether people can become infected with the new coronavirus, SARS-CoV-2, a second time. Small animal experiments suggest reinfection is unlikely, but right now, we don’t have a definitive answer.
Perhaps the most obvious place to focus is on related viruses, such as SARS.
A 2017 study of SARS patients found that 89% of people who recovered had detectable antibodies two years after the infection had cleared. However, at the six-year mark, this went down to just two out of 23 patients, suggesting people have immunity, but perhaps not indefinitely.
Our best hope will be if a SARS-CoV-2 vaccine can be developed which will provide rapid immunity.
[Related reading: How long before there’s a coronavirus vaccine?]