Posted on 14 October 2020
A 25 year-old man in the US state of Nevada has tested positive for COVID-19 for the second time, with symptoms reportedly more severe than during the first infection.
The possibility of reinfection with Sars-CoV-2 is not well understood. Given that immunity to other coronaviruses can trail off after 2-3 years, it was always suspected that immunity to COVID-19 would not be permanent. What is concerning about this case is just how quickly the same person was able to be reinfected. Here is the timeline of events:
Let’s take note of a few things here. Firstly, the patient tested negative twice in between his two positive tests. Furthermore, a case study published in The Lancet found that the viral samples taken at each infection were genetically distinct enough to suggest that he had been infected on two separate occasions (rather than the same infection resurfacing).
Secondly, he was able to be reinfected within two months, despite having clear symptoms during the first infection, and his symptoms during the second infection were worse. He had no known health problems or immune defects that would make him particularly susceptible to COVID-19. It’s also worth noting that his second set of symptoms emerged a mere two days after he tested negative.
What does all this mean? Well, it’s confirmation that immunity to COVID-19 has the potential to be very short-lived, even if you were symptomatic. It also suggests that the second infection has the potential to be more severe, though it isn’t yet clear why. It’s possible that the patient was simply exposed to a higher initial ‘dose’ of virus the second time around. The more concerning possibility is that the initial immune response made the second infection worse. This has been known to occur in some other viral infections like dengue fever.
While this case is definitely worrying, we shouldn’t be drawing any broad conclusions. Reports of second infections remain very rare, and with over 37 million confirmed cases to date, we would expect to have seen many more reinfections if such short-lived immunity was the norm. This is also the first report of a second infection being more severe than the first. Nevertheless, this case reinforces the point that we are still in the dark when it comes to understanding immunity to COVID-19.
There is one important lesson for which this case should serve as a reminder: catching COVID-19 does not guarantee immunity, and a negative test does not guarantee that you don’t have COVID-19. People in either of these groups should continue to follow social distancing and hygiene precautions as if they were still at full risk of catching or transmitting the virus.