The initial South Africa data from 12 patients also showed that considerable immunity is retained in individuals who were fully vaccinated and had been previously infected.
Six of the participants had no previous record of SARS-CoV-2 infection nor detectable nucleocapsid antibodies indicative of previous infection.
There was an observed 41-fold decline in vaccine-induced neutralizing antibodies compared to the ancestral strain of the virus, the researchers said.
However, those with previous infection who had received two doses of the vaccine were mostly able to neutralize the variant and had higher levels of antibodies.
The results, the international authors wrote in an online manuscript, showed “much more extensive escape” but incomplete escape in those people.
“Previous infection, followed by vaccination or booster is likely to increase the neutralization level and likely confer protection from severe disease in omicron infection,” they concluded.
The study did not include people who had received booster doses.
“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,” Africa Health Research Institute executive director Willem Hanekom said in an accompanying statement.
The research has been submitted to preprint server medRxiv and the results have not been peer-reviewed.
Responding to a tweet from Africa Health Research Institute professor Alex Sigal detailing the results, World Health Organization (WHO) chief scientist Soumya Swaminathan said a drop in antibody response of vaccinated people to the variant of concern had been expected.
“As expected, large drop in neutralization of #OmicronVirus by Biontech vaccinated sera. This does not mean the vaccines will not work- T cell immunity likely to persist. Await more studies,” she tweeted.
The WHO has said current vaccines remain effective, even as cases in South Africa have surged.
All of this comes a day before vaccine-makers Pfizer and BioNTech announced Wednesday that three doses of their vaccine “neutralize” the variant and that two doses “show significantly reduced neutralization titers.”
“Data indicate that a third dose of BNT162b2 increases the neutralizing antibody titers by 25-fold compared to two doses against the omicron variant; titers after the booster dose are comparable to titers observed after two doses against the wild-type virus which are associated with high levels of protection,” the companies said in a joint statement.