A study shows that cases in Europe and threaten year-end festivities are more than five times higher than the risk of a omicron coronavirus variant.
The results of the study by Imperial College London were based on the UK Health Security Agency and National Health Service data on people who tested positive for COVID 19 in a PCR test in England between November 29 and Dec. 11.
The study said that there was no evidence for the risk of hospitalization attendance and symptom status of omicron having different severity from delta. The data on hospitalizations is very limited, it said.
The study, which was dated Dec. 16, found that omicron was associated with a 5.4 fold higher risk of re-infection compared to delta when controlling for vaccine status, age, sex, ethnicity, asymptomatic status, region and specimen date.
Imperial College ICL said in a statement that the study had not yet been peer reviewed by the protection afforded by past infection against omicrons may be as low as 19%.
The researchers found a significant increase in the risk of developing a symptomatic omicron case compared to delta for those who were two or more weeks past their second vaccine dose and two or more weeks past their booster dose.
This translates into vaccine effectiveness of between 0% and 20% after two doses and between 55% and 80% after a booster dose.
Professor Neil Ferguson said in the statement of the ICL that the study provides further evidence of the very substantial extent to which omicrons can evade prior immunity given by both infection or vaccination.
Omicron poses a major, imminent threat to public health because of this level of immune evasion. But Dr Clive Dix, a former Chair of the UK Vaccine Taskforce, said it was important not to over-interpret the data.
The conclusions are based on making assumptions about omicrons where we don't have enough data, Dr Dix said. We don't have any data on the cellular immune response, which is now probably driving the effectiveness of vaccines. This is a crucial missing assumption in the modeling. He said that the conclusions are different from the data emerging from South Africa, where vaccines are holding up well against severe disease and death at present.
He said that there is a lot of uncertainty in these modeled estimates, and we can only be confident about the impact of boosters against omicron when we have another month of real-world data on hospitalization ICU numbers and deaths.
A study by Britain's SIREN looking at reinfection risk in health workers was carried out before omicron and found that a first coronaviruses gave 85% protection from a second for the following six months.
The data analyzed by Imperial College was based on 333,000 cases, including 122,062 of delta and 1,846, which were confirmed as the omicron coronavirus variant through genome sequencing.
The study, co-managed by Imperial College's professor Azra Ghani, described it as essential for modeling the likely future trajectory of the omicron wave and the potential impact of vaccination and other public health interventions. The new findings could lead to tighter restrictions across a number of European countries in a bid to stem the spread of the new variant.