A Spanish health care worker has reportedly tested positive for two variants of COVID-19 just 20 days apart — the shortest-known interval between infections.

The 31-year-old woman, who was fully vaccinated and boosted, tested positive with the Delta variant in late December and then with Omicron in January, the BBC reported, citing Spanish researchers.

She did not develop any symptoms after her first positive PCR test, but developed a cough and fever less than three weeks later, so she decided to get another test.

Experts said her case shows that people can get infected multiple times even if they have been fully jabbed against the bug.

Dr. Gemma Recio, the study’s author, told the European Congress of Clinical Microbiology & Infectious Diseases that the case highlighted that Omicron can “evade the previous immunity acquired either from a natural infection with other variants or from vaccines.”

She said that “people who have had COVID-19 cannot assume they are protected against reinfection, even if they have been fully vaccinated.

“Nevertheless, both previous infection with other variants and vaccination do seem to partially protect against severe disease and hospitalization in those with Omicron,” added Recio, of the Institut Catala de Salut, Tarragona in Spain.

Reinfections surged in December 2021 after the much more infectious Omicron variant emerged, and there was another spike when a slightly different version of it, dubbed BA.2, emerged in early March.