A healthcare worker was infected with Covid-19 twice in the space of 20 days in what is believed to have been the shortest time between two infections since the pandemic began.
The 31-year-old woman from Spain became infected with the Delta variant followed by the Omicron variant of the virus in under three weeks.
Researchers said the case shows that even vaccinated people who have had Covid-19 "cannot assume they are protected against reinfection".
The woman, who has been kept anonymous, became infected in December 2021, 12 days after she received her Covid booster vaccine.