A: So far it seems that short-term re-infection with SARS-CoV-2 is possible, but (hopefully) rare.
A key question from the beginning of the pandemic has been what is the duration of immunity for SARS-CoV-2. Viruses like measles can provide lifelong immunity, but immunity to seasonal coronaviruses has generally been short-lived (around 12 months).
One challenge is that it is difficult to pick-up cases of re-infection unless we are following and testing the same person regularly over time. The first case of confirmed re-infection was detected by chance from a patient in Hong Kong, a 33-year-old male who was tested at the airport upon re-entry from a visit to Spain. He had previously had a mild case several months earlier and was asymptomatic with his second infection, which was confirmed as a different strain from his first with viral genome sequencing. Interestingly, this patient had not produced detectable antibodies after his first mild infection. The patient’s viral load in his second infection was high enough to suggest he could pass on the infection to others.
A recent study described the first confirmed case of SARS-CoV-2 in the U.S—a 25-year-old male who had PCR confirmed infection in April, recovered and tested negative twice. 48 days after the initial test, he tested positive again. Genetic sequencing of the first and second infections also suggested these were different infections. Unfortunately, in this case the second infection was *more* severe than the first and required hospitalization.
Only three additional cases of *confirmed* re-infection have been documented, a 51-year-old female in Belgium with a milder case after 3 months, and a 46-year-old male in Ecuador with a worse case than his first infection two months prior. An 89-year-old woman in the Netherlands died during the course of her second infection.
Because there have been millions of SARS-CoV-2 infection worldwide it could be heartening that we only have 5 confirmed cases of re-infection. This does *suggest* that re-infection over a short time period may be rare, but in reality, it is hard to know how many re-infections we might be missing.
Especially if re-infections are more likely to be asymptomatic, those individuals may never seek out testing and thus would be less likely to document compared to those who have symptoms upon a re-infection. As time goes on, we will continue to learn more about how common or uncommon re-infection is, but it will be difficult to get accurate estimates without routine community testing.
What are the implications for our individual and collective battles against COVID-19 going forward?
• While immunologists still believe that natural immunity to SARS-CoV-2 should last at least several months and provide some protection from severe disease even upon re-infection, those previously infected should not consider this an “immunity passport.” You should still use precautions like masks and physical distancing to avoid re-exposure to SARS-CoV-2 *and* the possibility of transmitting it to others.
• These findings, along with recent evidence from the UK on declining antibodies at the population level, suggest that collectively we cannot rely on immunity from natural infection to confer herd immunity. Not only is such a strategy deadly (see previous post), without durable immunity it would be ineffective. Vaccines can induce stronger and more robust immunity and can be administered at regular intervals to safely maintain individual and herd immunity.
*Short-term* re-infection with SARS-CoV-2 is possible, but hopefully rare. Beyond several months, we expect re-infection will become more common as it does with seasonal coronaviruses.
Whether you’ve been previously infected or not, #StaySMART and do your best to minimize transmission.
Those Nerdy Girls
Link to excellent summary of re-infection by immunologist Dr. Akiko Iwasaki