A study has found that people who have been fully vaccinated or just recovered from Covid have virtually no antibody protection against the Omicron variant.

People who are double-vaccinated and those who have recovered from infection by previous strains of the SARS-CoV-2 virus have virtually no antibody protection against the Omicron variant, according to a study.

The research, recently published in the journal Allergy, found that only individuals vaccinated with a third or booster dose of the Covid-19 vaccine form antibodies that can partially block Omicron. Researchers from the Medical University of Vienna examined an Austrian subpopulation of vaccinated and recovered individuals for their antibody status and protection against the Wuhan, Delta and Omicron variants.

The findings show that both Covid-19 convalescent individuals and individuals who had been vaccinated twice developed antibody protection against Delta.

However, the antibodies were not able to block the receptor binding domain against Omicron, the researchers said.

The study found that blockade of Omicron was better in those individuals who had received the third vaccination.

"The third vaccination developed protective antibodies in many individuals. However, there is also a significant proportion (20 per cent) in whom no protection was established," said Rudolf Valenta, who led the research team.

The RBD differed only slightly in all previously known SARS-CoV-2 variants so that infections with these and the currently available vaccines provided protection against the previous variants, the researchers said.

Omicron is the first variant that differs greatly from the previous variants in RBD. Consequently, infections with the previous variants and currently available vaccines provide little or no protection against Omicron, they said.

The researchers noted that the best protection would be to develop a broadly effective combination vaccine that protects against both the previous variants and Omicron.

"Until we have such a vaccine, only repeated vaccinations with the existing vaccines will provide some protection," Valenta said.

"The protective effect achieved by vaccination can be evaluated with special tests that can be rapidly adapted to new virus variants," the immunologist added.