Two-thirds of omicron cases are reinfections, UK study suggests

Among 3,582 people who tested positive for COVID-19 in England between Jan. 5 and Jan. 20, nearly 65 percent said they had a prior bout with the virus that was confirmed by a test, according to a preprint study released Jan. 26 

The findings are part of Imperial College London's ongoing COVID-19 monitoring study, known as React, and are based on the results of 100,607 polymerase chain reaction test results from Jan. 5 to Jan. 20. About 3,582 participants out of 4,011 who had positive results reported their previous history of coronavirus infection; of these, about 65 percent had previously had COVID-19. Another 7.5 percent said they had a suspected prior infection, though it was not confirmed by a test. However, these results "are based on self-reported data and therefore it's uncertain what proportion of these are reinfections or recent infections picked up due to the sensitivity of PCR testing," researchers said

During this period in January, the study found 1 in 23 people or 4.41 percent were infected, the highest prevalence of positive test results since the study began in May 2020.

 Additionally, researchers found 99 percent of 1,406 positive test swabs that were sequenced were omicron, while just 1 percent were delta, and they found a high prevalence of infection among children aged 5 to 17. 

"We observed unprecedented levels of infection with SARS-CoV-2 in England in January 2022 and almost complete replacement of delta by omicron," researchers said.

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