DR Abraar Karan, an infectious disease doctor at Stanford University in California, suffered the same fate as many people in January. Despite being vaccinated and boosted, he got infected with Covid-19 during the surge of the highly infectious Omicron variant. Then, just a few months later in May, he performed a routine Covid-19 test one day before work and found himself infected with the coronavirus yet again.
Earlier in the pandemic, scientists held out the hope that hybrid immunity – the dual protection afforded by having been both infected with the virus and vaccinated against it – would provide the strongest shield against subsequent reinfection. The theory largely held true for versions of the virus that were less infectious than Omicron.