If you are unlucky enough to have had an intimate encounter with the dreaded Sars-CoV-2 virus, I’m afraid your love for him might not have been the last. Get ready for the second round (and the third, and maybe the fourth, maybe to infinity). Welcome to the Great Reinfection.
In the early months of the pandemic, reinfections were a notable rarity, even world news when they were discovered. “When the pandemic started, everyone assumed that once you got it, you were done,” says Juliet Pulliam, director of the South African Center for Modeling and Epidemiological Analysis DSI-NRF at Stellenbosch University.
Two years and some changes, this novelty has largely evaporated. A perfect storm of waning immunity, loose restraints and an extremely transmissible variant that makes the rounds has made reinfections the new norm for many. But even leaving these factors aside, it makes sense that there are more reinfections now than ever before. At this stage of the pandemic, recurrent infections would always have been more frequent than before, due to the large number of people who have had Covid-19. It cannot be re-infected unless it has already been infected in the first place.
Beyond these basic maths, it’s no surprise that reinfections occur, says Aubree Gordon, an infectious disease epidemiologist at the University of Michigan. “The virus has changed a lot,” he says. If you got infected with an earlier variant, Omicron is like this variety that wears and wears makeup, making it almost unrecognizable to our body’s immune defenses and harder to avoid.
But if reinfections are now an integral part of the future of the pandemic, how common are they? It is difficult to determine an exact figure, thanks to a drop in tests and reports which has made monitoring all types of Sars-CoV-2 infections much more complicated. Also, not everyone defines reinfection in the same way; UK health authorities, for example, require at least 90 days to elapse between a first and a second infection for this to count as a reinfection. Others, such as the European Center for Disease Prevention and Control, use a minimum of 60 days between infections.
In England, nearly 900,000 possible reinfections have been identified since the start of the pandemic. Of these, more than 10,000 were a third infection and almost 100 were a fourth.
Pulliam’s own work has attempted to put a figure on how many infections are actually reinfections. She and her team found that as of last week, about 15 percent of current infections in South Africa are reinfections. “And that’s almost certainly an understatement,” he warns, “because our surveillance isn’t great and we’ve probably missed a lot of people’s first infections.” But to respond to the prevalence of reinfections, in the grand scheme of things, Pulliam uses two words to sum it up: quite rare.
She and her team have also investigated the extent to which Omicron has shaken things up. They began monitoring reinfections towards the end of the beta wave in South Africa (which peaked in January 2021), targeting more than 100,000 suspected reinfections. They found that the protection offered by an initial infection against reinfection remained the same throughout the Beta wave and throughout the Delta wave which peaked the following July. And then it hit Omicron. The risk of reinfection steadily increased and stabilized at a higher number.
