Ask an expert: What are the chances of getting COVID-19 a second time?
Q: My husband is in a nursing home. He caught COVID there, recovered, and has now been testing negative. What are the current evidence-based statistics about getting it twice?”
Yvonne Cryns, Paso Robles
A: Reinfection seems to be possible, but so far, very few cases have been identified. More importantly, we need much more research and data about this virus in order to come to any proper conclusions.
If there is a key message about reinfection with COVID-19, it is that we should be concentrating on avoiding infection in the first place. And we know exactly how to do that.
Let’s begin with the statistics. The global case count for COVID-19 is roughly 32 million, but we know this not does not represent every infection. The same is true for the number of deaths, which has now surpassed 1 million. The big caveat is that both are severely undercounted, including in the U.S.
Both infections and mortality are also open to all sorts of problems, most notably the high rate of asymptomatic infections that are not tested or diagnosed, mild infections that may not be diagnosed and cases that fall through the cracks because of a lack of testing capability in many jurisdictions.
A similar approach can be applied to the statistics for reinfection rates. At the moment, there are about five confirmed cases of reinfection globally, two from the U.S. If we do the math according to this data, the chances of reinfection are almost zero (1.6x10-7 to be exact).
But that number should not be interpreted as zero risk, but it does seem infrequent, at least from the evidence we have to date.
Given the caveats above, and because we know relatively little about this virus and its mechanisms, it is still unclear how frequently reinfections may occur, the conditions that precipitate reinfection and who might be at elevated risk for reinfection. The take-home message is that people should not assume that if they have been infected, they have lifelong immunity.
The antibodies that are produced following infection with SARS-CoV-2 spike after the first few weeks and wane after a few months. That is normal and observed with other infections as well. What that does not tell us, however, is the resulting impact on immunity to this virus. In most of the confirmed reinfections, the second infection was associated with less severe symptoms or asymptomatic presentation.
Based on that limited evidence and what we know from other infections, we can infer that antibodies that are developed as a result of infection do seem to confer some level of immunity. How effective the antibody response might be or how long protection lasts over the longer term, however, remains unknown. What we do know is that infection is not a binary event whereby one is simply infected or not infected. Immune responses and mechanisms are highly variable across people. It is therefore difficult to predict severity of COVID-19 outcomes among infected people, even though we have identified some factors that contribute to increased risk.
To complicate matters, at least one of the confirmed reinfections seems to have caused more severe symptoms the second time around. We know this patient’s second infection was distinct from the first, based on sequenced virus samples from both of his infections. Given the 80 or more distinct genotypical variants of this virus, it could be that the reinfection made him sicker because the second strain was more potent, or he was infected with a higher viral load the second time.
The number of variants also raises concerns about vaccine development, though even a vaccine that is short-term, provides incomplete protection or requires booster shots would be helpful at the population level. For example, a vaccine that results in less severe infections for half the population would be a game-changer for this pandemic, in terms of preventing severe outcomes and deaths.
For the moment, we should be concerned primarily with doing whatever we can to keep ourselves from contracting SARS-CoV-2.
Dr. Aydin Nazmi is an epidemiologist and professor at Cal Poly SLO, where he serves as Presidential Faculty Fellow to COVID-19 Response and Preparedness. Send your questions to aydin@epi-intel.com.