LONDON, Dec 22 (Reuters) - The risk of needing to stay in hospital for patients with the Omicron variant of COVID-19 is 40% to 45% lower than for patients with the Delta variant, according to research by London"s Imperial College published on Wednesday. "Overall, we find evidence of a reduction in the risk of hospitalisation for Omicron relative to Delta infections, averaging over all cases in the study period," the researchers said of the study, which analysed data from PCR-test confirmed cases in England between Dec. 1 and Dec. 14. Scientists are racing to answer questions about the virulence and severity of Omicron to help governments respond to the variant, which is spreading at breakneck speed. The British research follows a South African study on Wednesday which found that people diagnosed with Omicron in South Africa between Oct. 1 and Nov. 30 were 80% less likely to be admitted to hospital than those diagnosed with another variant in the same period. read more Imperial College researchers said the risk of any visit to hospital with Omicron was between 20% and 25% lower than with Delta. However, they added that the reductions in hospitalisation must be balanced against the larger risk of infection with Omicron, due to the reduction in protection provided by both vaccination and natural infection. Britain reported more than 100,000 new cases of COVID-19 on Wednesday for the first time since widespread testing was available. They said their estimates from the research suggested that people who had received at least two vaccine doses remained substantially protected against hospitalisation, even if protection against infection has been largely lost against the Omicron variant.