Spanish researchers say this is the shortest known interval between two coronavirus infections.
A 31yearold health worker in Spain has contracted Covid twice in just 20 days the shortest time between infections ever detected, according to Spanish researchers.
Tests show the woman was infected with two different strains Delta in late December and Omicron in January.
According to the researchers, this shows that people who have been through Covid cannot assume that they are protected from being infected again, even if they are also vaccinated. However, they point out that vaccination and previous infection appear to increase protection against serious illness and hospitalization in people with a micrometer.
It is difficult to know exactly how many people have been reinfected with Covid during the pandemic, as only full genome sequencing can confirm that infections are caused by different strains.
In the UK, authorities classify reinfections as cases where a person tests positive within a period of at least 90 days. Based on that definition, health officials say nearly 900,000 people may have been infected twice with Covid as of early April.
The Spaniard had no symptoms after her first positive PCR test, but less than three weeks later she developed a cough and fever, prompting her to have another test.
When the tests were analyzed further, they showed that the patient was infected with two different strains of coronavirus.
In a presentation at the European Congress of Clinical Microbiology and Infectious Diseases, study author Gemma Recio said the case shows that the omicron is able to “evade previous immunity caused by natural infection with other variants or by vaccines was purchased”.
“In other words, people who have been through Covid19 cannot assume that they will be protected from reinfection even if they have been fully vaccinated,” says Recio of the Institut Catala de Salut, Tarragona, Spain.
“However, both previous infections with other variants and vaccinations in people with microns seem to partially protect against serious illness and hospitalization.”
She said monitoring for reinfections in fully vaccinated people is important and can help look for variants that evade vaccines.
Covid reinfections rose sharply in December 2021 after the much more contagious Omicron variant emerged. And there was another spike in cases when a slightly different version of the Omicron called the BA.2 surfaced in early March.
Before that, 1% of all reported cases in the UK were flagged as secondary infections but now that percentage has risen to 11%.
Most are likely humans infected with the Alpha or Delta variants and then reinfected with the more contagious Omicron.
Some scientists predict that everyone will eventually contract Covid twice, and then likely many more times in their lifetime.