Researchers say it's the shortest-known gap between two coronavirus infections.
The Spaniard did not develop any symptoms after her first positive PCR test, but less than three weeks later she developed a cough and fever which prompted her to take another test.
In a presentation at the European Congress of Clinical Microbiology and Infectious Diseases, study author Dr. Gemma Recio said the case highlighted that Omicron can "evade the previous immunity acquired either from a natural infection with other variants or from vaccines". "Nevertheless, both previous infection with other variants and vaccination do seem to partially protect against severe disease and hospitalisation in those with Omicron," added Dr Recio, from the Institut Catala de Salut, Tarragona in Spain.
Covid reinfections rose sharply in December 2021 after the much more infectious Omicron variant emerged, and there was another increase when a slightly different version of it, called BA.2, appeared in early March.