Question: I read this article from NPR, “Scientists Confirm Nevada Man Was Infected Twice With Coronavirus,” with interest and disappointment. If it’s proven that folks can get reinfected with the virus just a couple months after the first infection, doesn’t this bode poorly for the efficacy of a vaccine?

Answer: This Monday, Lancet published a case study of the first confirmed COVID-19 reinfection in the United States. This case study adds to a small but growing body of evidence that reinfection can occur. In my opinion, the main take-away is that even if you have already been infected with SARS-CoV-2, you should still continue to practice public health prevention measures — masks, distancing, hand washing. When it comes to vaccines, the take-away is less clear cut; I suggest setting aside your disappointment until we know more. Here’s the deal, as synthesized from an accompanying commentary that Lancet published, “What reinfections mean for COVID-19,” as well as an article published in Scientific American three weeks ago, “What COVID-19 reinfection means for vaccines,” and an article published in Naturelast month, “Coronavirus reinfection: three questions scientists are asking.”

• What are the odds of reinfection? So far, we have very few case studies to draw inferences from (N=5). Is this because reinfection is truly extremely rare or because we are only now in a position to experience and monitor reinfection (because time has elapsed, 2nd waves are occuring, and testing/genomic analysis systems are more widely available)? We need more time and data to know the answer. Based on current evidence, the odds of reinfection seem miniscule, but absence of evidence is not evidence of absence. Reinfection for other types of coronaviruses is the norm.
• Why does reinfection occur? We don’t know. One hypothesis is that reinfection occurs in those who have limited antibodies after first infection. Another is that antibody response quickly wanes, leaving an individual unprotected against future exposure. We need to measure the level of antibodies present at time of reinfection to test these hypotheses.
• Are people less likely to experience severe disease upon reinfection? So far, it’s a mixed bag. Of the five cases, two experienced more severe disease upon reinfection. Of course, there are likely a number of people reinfected asymptomatically, who likely wouldn’t show up in estimates, so these few cases we have monitored are already biased towards those with severe disease and come to the hospital. Among the two cases who did experience more severe disease upon reinfection, we still don’t know why. Were they exposed to higher levels of the virus? Were there changes to their underlying health? Did a variant of SARS-CoV-2 produce more severe disease? Did their immune system somehow make things worse, like through an antibody-dependent enhancement? We need more data.
• Does infection by different viral isolates mean we need a vaccine for each type? As written in the Lancet commentary, “There is currently no evidence that a SARS-CoV-2 variant has emerged as a result of immune evasion. For now, one vaccine will be sufficient to confer protection against all circulating variants. Furthermore, reinfection by a distinct viral variant from the original virus does not imply immune escape.” Note: “immune escape” aka “immune evasion” is the ability of a virus to evade a person’s immune system and continue to grow/spread.
• Can those who are reinfected spread the virus to others? Limited data point to yes, based on viral load detected among those reinfected. We do not, however, have any case studies of a reinfected person transmitting infection.
• What does reinfection mean for vaccine development? We need more information on reinfection to really answer this question. That said, based on what we currently know, it’s looking possible that we may need to have booster shots as our immunity wanes and/or we may need to have new generations of the vaccine to respond to new variants (as we have with flu). These developments would mean more logistic hurdles, which are surmountable. If we do see far more reinfections and more severe outcomes upon reinfection, the possibility that SARS-CoV-2 tampers with our immune memory increases, and this would have far more problematic vaccine ramifications. Given the vaccine trials underway and the safety data collected to date, this possibility seems extremely unlikely. Finally, vaccine induced immunity is more powerful than immunity induced by natural exposure. As Yale professor of immunobiology, Dr. Iwaskai, told NPR, “The good thing about a vaccine is that it can induce much better immunity, a much longer lasting immunity, than the natural exposure to the virus.” If we’re lucky, one shot will do the trick!