Brits are being urged to get their boosters as new analysis shows two vaccine doses offer little protection against symptomatic Omicron infection.
The latest research by the UK Health Security Agency (UKHSA) found 20 weeks after a second dose of AstraZeneca there is no effect against symptomatic Omicron.
For people who received two doses of Pfizer or Moderna, effectiveness dropped from around 65 to 70% down to around 10% by 20 weeks after the second dose.
Two to four weeks after a booster dose, effectiveness ranged from around 65 to 75%, dropping to 55 to 70% at 5 to 9 weeks and 40 to 50% from 10 weeks after the booster.
But the UKHSA said one dose of any vaccine saw a 35% reduced risk of hospital admission.
Unvaccinated people with Omicron are up to eight times more likely to end up in hospital than those who are boosted, it said.
The latest analysis offered an encouraging assessment of the new variant's severity - as people who catch it are one third less likely to enter hospital than those who catch Delta.
Last week the UKHSA estimated Omicron sufferers were 31% to 45% less likely to attend A&E than Delta, and 50 to 70% less likely to be admitted to hospital.
Today it's new analysis was more optimistic - finding the risk of attending A&E or being admitted was 43-50% lower, and the risk of full hospital admission was between 63% and 70% lower.
Health Secretary Sajid Javid said: "This is more promising data which reinforces just how important vaccines are. They save lives and prevent serious illness.
"This analysis shows you are up to 8 times more likely to end up in hospital as a result of COVID-19 if you are unvaccinated.
"It is never too late to come forward for your first dose and it’s vital that everyone comes forward to get boosted now as we head into the new year."
UKHSA Chief Medical Adviser Dr Susan Hopkins said the analysis was in keeping with "encouraging signs" we have already seen.
But she added: "It remains too early to draw any definitive conclusions on hospital severity, and the increased transmissibility of Omicron and the rising cases in the over 60s population in England means it remains highly likely that there will be significant pressure on the NHS in coming weeks.
"The data once again shows that coming forward for your jab, particularly your third dose, is the best way of protecting yourself and others against infection and severe disease."
