LONDON — Booster jabs will be offered to everyone over 18 in England from this week, British Prime Minister Boris Johnson has announced, as he declared an "Omicron emergency", BBC reported.

"No one should be in any doubt, there is a tidal wave of Omicron coming," Boris Johnson said in a TV statement on Sunday evening.

The target to offer a booster to all adults by the end of January will be brought forward by a month, he said.

Some medical appointments may also be postponed to focus on boosters.

Johnson gave his update on Sunday evening - just hours after the UK's Covid alert level was raised to four due to the spread of the new Omicron virus variant.

Level four means a high or rising level of transmission - and the last time the UK was at level four was in May.

"I'm afraid we're now facing an emergency in our battle with the new variant Omicron," said Johnson.

"It is now clear that two doses of vaccine are simply not enough to give the level of protection we all need. But the good news is that our scientists are confident that with a third dose, a booster dose, we can all bring our level of protection back up."

He added: "At this point our scientists cannot say that Omicron is less severe.

"And even if that proved to be true, we already know it is so much more transmissible that a wave of Omicron through a population that was not boosted would risk a level of hospitalisation that could overwhelm our NHS and lead sadly to very many deaths."

The new booster target means people aged 18 and over in England will be able to get their third jabs from this week - as long as it has been three months since their second dose.

People aged 30 and over can already book an appointment in advance using the online service from two months after their second dose and over-18s in this position will be able to book from Wednesday.

Some walk-in appointments will be available from Monday for eligible over-18s, depending on location.

Scotland is also setting the same target and aiming to offer all adults a booster by the end of the year, and Northern Ireland said it is stepping up its rollout and hopes to get as many people as possible boosted by then.

But Johnson said in order to reach the new jab target, certain other medical appointments would need to be postponed to the New Year. Some GPs are already allowed to postpone routine health checks to make space for vaccinations.

Early data shows that getting a third booster dose prevents about 75% of people getting any Covid symptoms from Omicron.

More than half a million booster jabs and third doses were given in the UK on Saturday - the second day that has happened since the booster rollout began.

A further 1,239 new cases of Omicron were announced in the UK on Sunday, bringing the total number of UK Omicron cases to more than 3,000 - although the real number is estimated to be much higher.

Labour leader Sir Keir Starmer reiterated Johnson's call to "get boosted" - adding: "So much has been asked of the British people, and time and again you have risen to the challenge. So let's keep our foot on the pedal and get Britain boosted to protect our families, friends and NHS."

Scotland and Northern Ireland have already opened up boosters to over-30s - and those aged 18 to 29 in Scotland can get their booster jabs from later in the week.

First Minister Nicola Sturgeon said Scotland had the highest rate of booster jabs of all the UK nations - but warned it was possible that further measures might be needed in the weeks ahead.

Earlier, the rules on self-isolation were updated again in England. From Tuesday, fully-vaccinated people who come into contact with a Covid will not need to automatically self-isolate - but instead take daily lateral flow tests for seven days.

It is the latest rule change, after the UK government brought in new Plan B measures - including Covid passports for some crowded events and asking people to work from home. Both Wales and Scotland have said new rules could come in the next few weeks.

Johnson's statement comes as the row continues over gatherings at Downing Street during last year's coronavirus lockdown.