Patients with Omicron less likely to be admitted than those with Delta variant.

Patients who have Omicron variant of the covid-19 are less likely to be admitted than those with the Delta variant, a study by UK Health Security Agency (UKHSA) has shown.

Those with Omicron are estimated to be between 31% and $5% unlikely to visit accident and emergency department compared with those with Delta , and between 50% to 70% less likely to require admission to hospital, according to the UKHSA. The early findings, described as "encouraging" and "promising, are consistent with analysis published on Wednesday by Imperial College London and the University of Edinburgh.

However, health leaders also warned that cases in the UK continued to increase at an “extraordinary rate” and that the sheer numbers of people becoming infected could still result in a significant number of people becoming seriously ill, and the risk of the NHS becoming overwhelmed.

The Scientific Advisory Group for Emergencies (Sage) warned ministers that Omicron would have to be about 90% less severe than Delta for hospital admissions not to reach previous peak levels “unless the wave peaks early for other reasons”, according to minutes published on Thursday. Scientists and health officials remained concerned that any benefit of Omicron being milder could be wiped out by large numbers of people becoming infected.

The UKHSA said the new variant was more transmissible than previous ones such as Delta, and could still lead to significant numbers of people needing hospital treatment over the coming weeks.

At the same time, the preliminary UKHSA data suggests that protection against Covid starts to wane 10 weeks after a booster jab, raising the prospect that a fourth dose of vaccine may being required for some in 2022.

It has already been established that protection against symptomatic disease wanes after a second dose of vaccine, and then improves after a booster. However, the new UKHSA data suggests this extra protection starts to decrease more rapidly against Omicron than Delta, being about 15% to 25% lower from 10 weeks after the booster dose.

Health officials stressed that although there were insufficient numbers of severe cases of Omicron as yet to analyse vaccine effectiveness against hospitalisation, this was more likely to be sustained, particularly after a booster. One official said the “vast majority” of over-60s received their booster between eight and 10 weeks ago.

The Joint Committee on Vaccination and Immunisation, the body that would decide on whether a fourth dose is required, has begun assessing the UKHSA data. One health official suggested that a first dose of a new vaccine specially targeted at Omicron might be a “better option” than a fourth dose of the same vaccine.

The new data emerged after the UK experienced yet another record-breaking number of daily reported Covid cases, with 119,789 reported as of 9am on Thursday.

The UKHSA said Omicron now accounts for 76% of Covid cases in England, making it the dominant variant. The areas with the highest rates of Omicron are London (90.2%) and the east of England (80%), while the lowest are the north-east (56.8%) and Yorkshire and Humber (71%).

Dr Jenny Harries, the chief executive of the UKHSA, said: “Our latest analysis shows an encouraging early signal that people who contract the Omicron variant may be at a relatively lower risk of hospitalisation than those who contract other variants. However, it should be noted both that this is early data and more research is required to confirm these findings.

“Cases are currently very high in the UK, and even a relatively low proportion requiring hospitalisation could result in a significant number of people becoming seriously ill. The best way that you can protect yourself is to come forward for your first two doses of vaccine, or your booster jab and do everything you can to stop onward transmission of the infection.”

The health secretary, Sajid Javid, said: “This new UKHSA data on Omicron is promising – while two doses of the vaccine aren’t enough, we know boosters offer significant protection against the variant and early evidence suggests this strain may be less severe than Delta.

“However, cases of the variant continue to rise at an extraordinary rate – already surpassing the record daily number in the pandemic. Hospital admissions are increasing, and we cannot risk the NHS being overwhelmed.”

The fast spreading Omicron variant is thought to have more hospitalisation rate than the two preceding variants. According to data from the US Centers for Disease Control and Prevention, Omicron accounts for roughly three-quarters of COVID-19 cases.

"Surely, we have learned by now that we underestimate this virus at our peril," Tedros Adhanom, director-general of the World Health Organization, said in Dec. 14 during a briefing. "Even if omicron does cause less severe disease, the sheer number of cases could once again overwhelm unprepared health systems."