Antibodies from the Pfizer vaccine may be up to 40 times less effective in providing protection against the fast-spreading Omicron variant, an initial study suggests.
Those double jabbed who have also recovered from being infected with Covid are likely to have the best protection from the strain, which was first recorded in South Africa in November, suggesting boosters will bring a benefit.
Vaccines are still likely to provide protection against severe disease and death from the variant.
The limited study analysed only 12 patients who had been double jabbed with the Pfizer vaccine, but is believed to be the first evidence about vaccine effectiveness against the new variant.
Professor Willem Hanekom, of the Africa Health Research Institute, which led the study, said: "The clinical implications of these important laboratory data need to be determined.
"It is likely that lesser vaccine-induced protection against infection and disease would be the result. Importantly, most vaccinologists agree that the current vaccines will still protect against severe disease and death in the face of Omicron infection. It is therefore critical that everyone should be vaccinated."
The World Health Organisation has said there is no indication that Omicron causes any more severe disease in an infected person than Delta, which is currently the dominant variant.
Because of the rapid nature of the spread of Omicron, vaccine experts and scientists across the world have been racing to find out more about how it behaves.
Today the number of Omicron cases hit 437 with 101 new infections have been confirmed - however the real figure is likely to be much higher than that.
Health Secretary Sajid Javid has confirmed there is community spread of the variant although travel red lists with certain countries remain in place.
Professor Tim Spector, from the Covid Zoe app, said that in around 10 days' time the UK could have more cases of Omicron than some countries it had put on the travel red list.
The professor of genetic epidemiology at King's College London told BBC Breakfast: "The official estimates are about 350-odd Omicron cases, and because the current testing is missing a lot of those, it's probably at least 1,000 to 2,000 I would guess at the moment.
"And we are expecting this to be doubling about every two days at the moment, so if you do your maths - say assumed it's 1,000 at the moment, and you think it's going to be doubling every two days, you can see that those numbers are going to be pretty (high) certainly in about 10 days time.
"By that time, we'll probably have more cases than they will in some of those African countries.
"So I think these travel restrictions do perhaps have their place initially, when cases are really low here and really high in the other country, but when we reach that equilibrium, there's very little point in having them in my opinion."
Pfizer and BioNTech did not respond to Bloomberg's requests for comment.
