The Omicron variant of coronavirus is largely resistant to antibodies from people who recover from COVID-19 infection, and those vaccinated with two doses of the Pfizer vaccine, according to a study.
The research, published in the journal Cell, also shows that several antibodies used to treat COVID-19 will be ineffective against Omicron.
However, a third dose of the Pfizer vaccine, and mixing Pfizer and AstraZeneca preventives may protect well against the variant.
The Omicron variant of SARS-CoV-2 appears to be spreading faster than any previous variant and may soon dominate globally, the researchers said.
In the study, they used non-hazardous virus-like particles that carry the Omicron spike protein and are well suited for analysis of virus entry and its inhibition.
The spike protein is used by the SARS-CoV-2 virus to enter and infect cells.
Currently, combinations of the antibodies Casirivimab and Imdevimab, and Etesevimab and Bamlanivimab are used to treat COVID-19.
However, the researchers showed that these antibodies are largely ineffective against the Omicron spike. Only one antibody, Sotrovimab, inhibited the Omicron spike, they said.
"Our cell culture studies suggest that most antibodies currently available for COVID-19 therapy will be ineffective against Omicron," said study first author Markus Hoffmann from German Primate Center.
"Sotrovimab is an exception and could become an important treatment option for Omicron-infected patients," Hoffmann said.
The researchers further investigated whether patients infected in Germany during the first wave of the pandemic had produced antibodies that protect against the Omicron variant.
While the antibodies inhibited the spike of the virus responsible for the first wave, the researchers had little effect against the Omicron spike.
They assume that these individuals do not have robust immune protection against the Omicron variant, although an inhibition by T cells, which are also produced during infection, remains to be analysed.
Antibodies produced after two immunisations with the Pfizer vaccine also inhibited the Omicron spike significantly less efficiently than the spike proteins of other variants, the researchers said.
A better protective effect was observed after three doses with Pfizer and after heterologous immunisation with AstraZeneca and Pfizer preventives, they said.
These results indicate that dual immunisation with Pfizer may protect less efficiently against the Omicron variant as compared to the Delta variant, according to the study.
Triple immunisation with Pfizer (booster) and cross-vaccination with AstraZeneca/Pfizer could establish stronger protection, it found.
"Our results indicate that antibody therapies for COVID-19 need to be adapted to the Omicron variant. Adaptation of the BioNTech-Pfizer vaccine should also be considered," said Hoffmann.
"In contrast, triple immunisation with BioNTech-Pfizer (booster) and cross-vaccination with Oxford-AstraZeneca," Hoffmann added.