Omicron more likely to reinfect than Delta, no milder -study
The risk of reinfection with the Omicron coronavirus variant is more than five times higher and it has shown no sign of being milder than Delta, a study showed, as cases soar across Europe and threaten year-end festivities.
The results of the study by Imperial College London were based on UK Health Security Agency and National Health Service data on people who tested positive for COVID-19 in a PCR test in England between Nov. 29 and Dec. 11.
"We find no evidence (for both risk of hospitalisation attendance and symptom status) of Omicron having different severity from Delta," the study said, although it added that data on hospitalisations remains very limited.
"Controlling for vaccine status, age, sex, ethnicity, asymptomatic status, region and specimen date, Omicron was associated with a 5.4-fold higher risk of reinfection compared with Delta," the study, which was dated Dec. 16, added.
The protection afforded by past infection against reinfection with Omicron may be as low as 19%, Imperial College (ICL) said in a statement, noting that the study had not yet been peer reviewed.
But Dr Clive Dix, former Chair of the UK Vaccine Taskforce, said it was important not to overinterpret the data.
"The conclusions made are based on making assumptions about Omicron where we still don't have sufficient data," Dr Dix said. "For example, we have no data on the cellular immune response which is now probably driving effectiveness of vaccines."
"This is a crucial missing assumption in the modelling."
Some of the conclusions are different to the data emerging from South Africa, where vaccines are holding up well against severe disease and death at present, he said.
"There is a huge amount of uncertainty in these modelled estimates and we can only be confident about the impact of boosters against Omicron when we have another month of real-world data on hospitalisation ICU numbers and deaths," he said.