COVID spring boosters give maximum protection and three million Brits have now had the top-up.
A study found the extra jab – being given to elderly and vulnerable people – gives even higher immunity than two or three doses.
Although Omicron is mild and hospital rates are falling, experts said the doses give a potentially life-saving boost to high-risk people and may also cut transmission.
Professor Saul Faust, trial leader at University Hospital Southampton, said: “We saw a really good boost up and beyond what had been achieved with a third dose.
“We know that very high antibody levels are one of the things that help us prevent immediate transmission.
“You’re going to want to keep up your sleeve the ability to boost people quickly if there were another variant. We don’t know yet what a future variant might be.”
Read more on Covid
He added that older people may get a fifth dose in the autumn and younger Brits could be boosted if Covid becomes severe again.
Prof Faust’s study, published in The Lancet Infectious Diseases, found the fourth dose of Pfizer or Moderna vaccine doubled anti-Covid antibody levels in older adults.
NHS England had given 3,021,162 spring boosters by Sunday and will send 200,000 more invites this week.
Head of the vaccine rollout, Steve Russell, said: “The latest phase of the vaccination effort continues at pace, with 130,000 people coming forward for their spring booster over the weekend alone.
“I would urge anyone yet to take up their extra boost to come forward as soon as possible to give you maximum protection from Covid throughout the coming months.”
It comes after Britain ranked 56th in a world league table of Covid deaths as health chiefs say 15million people died globally in 2020 and 2021.
A World Health Organisation report reveals the UK had 109 more deaths than usual per 100,000 people in the two years.
That is lower than Germany, Italy, Spain and the US — and way below Peru, which was worst with 437 excess fatalities per 100,000.
Scientists and Labour leader Sir Keir Starmer claimed our toll was the worst in Europe at the height of the crisis.
Read More on Trending In The News
The report says many countries under-counted Covid deaths and the global figure is between 13.3million and 16.6million — far higher than the official six million.
The UK was hit hard and early by the bug in 2020 but jabs brought a change of fortunes last year.
