A 31-year-old health worker in Spain contracted COVID-19 twice in a period of just 20 days – the shortest time among infections ever detected, according to Spanish researchers.
Tests show that the woman was infected with two variants – delta in late December and omicron in January.
This shows, according to the researchers, that people who have contracted the virus cannot be considered to be protected from reinfection, even if they have also been vaccinated. However, they note that vaccination and a previous infection appear to increase protection against serious disease and hospitalization in people with microns.
It is difficult to know exactly how many people have contracted Covid-19 again during the pandemic, because only complete genetic sequencing can confirm that the infection is caused by different strains.
In the UK, authorities classify re-infections as cases in which a person has tested positive within at least 90 days. Based on that definition, health officials say nearly 900,000 people have been infected twice with the Covid virus as of early April.
The Spaniard had no symptoms after her first positive test, but less than three weeks later she developed a cough and fever, which prompted her to take another test.
When the tests were analyzed further, they showed that the patient had contracted two different strains of coronavirus.
In a presentation at the European Conference on Clinical Microbiology and Infectious Diseases, study author Gemma Risio said the case shows that Omicron is able to “circumvent prior immunity acquired from natural infection with other variants or from vaccines.”
“In other words, people who have contracted COVID-19 cannot assume that they are protected from reinfection, even if they have been fully vaccinated,” says Ricio of the Instituto Catala de Salute in Tarragona, Spain.
“However, both previous infection with other variants and vaccination appear to partially protect against serious disease and hospitalization in micronized subjects.”
She said that monitoring reinfection in people who have been fully vaccinated is important and can help to look for variants that avoid vaccines.
Covid cases rose sharply in December 2021, after the emergence of the most contagious omicron variant. And there was another spike in cases where a slightly different version of omicron, called BA.2, appeared in early March.
Before that, 1% of all reported cases in the UK were classified as a second infection – but that percentage has now risen to 11%.
Most are likely to be people with alpha or delta variants and then re-infected with the more infectious oomicron.
Some scientists predict that everyone will eventually contract Covid twice, and then possibly several times in their lifetime.
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