A South African study shows that the vaccine may be less effective against Omicron than other strains of coronaviruses, but still offers a degree of protection.
The researchers from the African Health Research Institute said the vaccine's loss of immune protection was extensive but incomplete in the first published study.
The researchers took 14 samples from 12 people who had received two doses of the BioNTech vaccine and tested their ability to neutralise Omicron.
The Omicron infections resulted in a reduction in the amount of virus-blocking antibodies compared to the original strain that was found in Wuhan two years ago.
The authors of the study found that Omicron escaped neutralisation more than theBeta variant.
Alex Sigal, head of research at the laboratory, said that Omicron did not evade the vaccine despite the reduction in production.
The researchers reported that people who had been double-vaccinated and had previously been exposed to Covid-19 retained high levels of antibody protection. They said that it would likely give protection from severe disease.
The Omicron variant was first identified in South Africa in late November, raising concerns among health experts that it could evade existing vaccines.
The chief executive of BioNTech said the company would publish its own data later this week. He told NBC that he would be more hopeful.
The results suggested that a new class of Omicron-specific boosters would probably have to be developed.
It looks like what we would expect, going along with the many vaccine breakthrough cases that have already been reported with Omicron.
The professor of immunology at Imperial College London said the South African study raised hopes thatboosted people would typically be safe.
The study showed that people who had previously been exposed were all in the safe zone.
Jacob Glanville, the founder of Centivax, said that the study suggested that most double-vaccinated people would be at risk for Omicron.
Public health officials are asking people to boost their vaccinations because most won't have enough to effectively fight the disease.
Glanville said that T-cells would allow double-vaccinated people to retain protection against severe disease.
Morgan Stanley said the African Research Institute data suggested a significant drop in vaccine effectiveness against Omicron.
Matthew Harrison, an analyst at Morgan Stanley, believes the likelihood of a variant specific booster is increased.
The new variant would likely result in a material drop in vaccine effectiveness according to Stéphane Bancel, Moderna's chief executive.
Some samples showed almost no loss and some showed considerably more, according to researchers at Sweden's Karolinska Institutet.
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The average loss of neutralisation was lower than feared, which would make Omicron worse than Delta, but not as extreme as we expected, said one of the investigators. The researchers used a pseudoviruses to look like the new strain.
They said that neutralisation is not completely lost for all samples, which is positive, in the South African and Swedish studies.
The neutralisation assays can't predict whether a vaccine will work. Kate O'Brien, the head of vaccines at the World Health Organization, said on Tuesday that more complete studies on effectiveness would not be completed for some time.
Peter Wells is in New York.
