A European healthcare worker was infected with Covid-19 twice in the space of 20 days. This is believed to be 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 just under three weeks.
“Vaccinated people who have had Covid-19 cannot assume they are protected against reinfection,” researchers say of the case study.
The woman, who has been kept anonymous, became infected in December 2021, 12 days after she received her Covid booster vaccine. The first positive result was picked up through routine healthcare testing.
The healthcare worker had no symptoms and went into isolation for 10 days. Days after returning to work in January she began to show symptoms of Covid-19 – a cough and fever as well as feeling generally unwell – and took a test which yielded a positive result.
Lab tests showed that she was initially infected by the Delta variant of the virus which causes Covid-19, followed by the Omicron variant.
Her case, which is being presented to the European Congress of Clinical Microbiology and Infectious Diseases in Portugal, is believed to be the shortest known gap between infections.
Dr Gemma Recio, of the Institut Catala de la Salut in Spain, one of the study’s authors, said: “This case highlights the potential of the Omicron variant to evade the previous immunity acquired either from a natural infection with other variants or from vaccines,”
She continued: “In other words, people who have had Covid-19 cannot assume they are protected against reinfection, even if they have been fully vaccinated.”
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React, a UK study charting reinfection, swab-tested thousands of volunteers in England, and found some people are more susceptible to being reinfected.
The results revealed that healthcare workers and households where there are children or lots of people under one roof have increased risk of reinfection.
The study also revealed that two thirds of those who caught Omicron had previously had Covid.
Reinfection is understood as a second or subsequent Covid-19 infection. Work by the Office for National Statistics (ONS) suggests the risk of reinfection is 10 times higher with the Omicron variant compared with the Delta variant.
An ONS report also found reinfection is more likely among unvaccinated individuals, and when vaccine immunity starts to wane.
Professor Paul Hunter, an expert in infectious diseases at the University of East Anglia tells HuffPost UK: “Neither vaccination nor a prior infection provides permanent immunity to subsequent infections. Reinfections are going to become the norm fairly soon if they haven’t already.”
He adds: “Other coronaviruses cause repeat infections every three to six years on average, though evidence suggests that reinfection period is much shorter than this.”
Prof. Hunter cites a December 2021 Lancet study in which US biostatistician Professor Jeffrey P Townsend suggested that “reinfection by SARS-CoV-2 under endemic conditions would likely occur between three months and 5·1 years after peak antibody response, with a median of 16 months”.
“But that was before Omicron which reduced that period,” Prof Hunter says. “Reinfections will most likely occur with Omicron in some people less than three months after an initial infection. Nevertheless, a prior infection now provides better protection against an infection than vaccination.”
The UK Health Security Agency (UKHSA) actually defines reinfection as a case that’s 90 days or more after a previous confirmed Covid infection.
“This is to exclude infected individuals who continue to shed virus for a longer time after initial infection,” Professor Lawrence Young, a virologist and professor of molecular oncology at Warwick University, previously explained.