Jul 31, 2020: Vol 20 No 91
For how long does immunity against Covid-19 last in a person who has suffered and recovered from the disease? Experts say that nobody knows. This is actually untrue because it is now possible to make an educated guess.
Consider: The disease originated in China in December 2019. It was declared a pandemic on March 11, 2020. Although we have reached the end of July 2020, nobody, so far, has definitively been recorded to have suffered from the disease twice.
There have been several reports of persons continuing to test positive long after recovery from the disease, and instances of persons testing positive after recovery, with an interval during which they tested negative. However, these persons were not symptomatic during the later periods. It is possible that the later positive tests were false positives, or that the tests detected virus residue in biological samples. There was no confirmation that the virus present was viable and capable of replicating in new hosts.
There have also been reports of persons who appeared to have suffered a relapse of illness after a short interval of recovery. In all cases, the descriptions were consistent with incomplete recovery followed by subsequent worsening, rather than with reinfection.
Persons who recovered from Covid-19 in, say, March 2019, have probably continued to be exposed to the disease to the same extent as those who had not yet contracted the disease. Considering that there have been no conclusive reports of persons suffering from the disease twice, it suggests that these persons became immune and that the immunity has lasted to the present day; that is, for about 5 months.
Of interest, asymptomatic Covid-19 infection has also long been recognized, and there have been no reports of persons with asymptomatic infection developing the disease months later. This suggest that asymptomatic infection is also associated with immunity that lasts for several months.
The greater the passage of time without report of new illness in persons who were previously infected, the longer we know that the immunity lasts.