New research out of Europe has found that a booster dose of a COVID-19 vaccine could produce sufficient antibodies to .

Researchers from the Institut Pasteur and Vaccine Research Institute in France, together with KU Leuven in Belgium and Orléans Regional Hospital, Hôpital Européen Georges Pompidou (AP-HP), Inserm and the CNRS, also in France, studied the sensitivity of Omicron to antibodies.

The results showed that the Omicron variant appeared resistant to most monoclonal antibodies, or those , as well as antibodies produced in people fully vaccinated with the Pfizer-BioNTech and AstraZeneca vaccines or who were previously infected with COVID-19.

But after administering a booster dose of the Pfizer vaccine, or a single vaccine dose to those previously infected, the researchers found this led to a "significant" increase in antibodies, sufficient to neutralize Omicron.

"We now need to study the length of protection of the booster dose," said Olivier Schwartz, co-author of the study and head of the virus and immunity unit at the Institut Pasteur.

"The vaccines probably become less effective in offering protection against contracting the virus, but they should continue to protect against severe forms."

While believed to be more transmissible than the previous Delta variant, and capable of spreading to those who are vaccinated or have been previously infected, evidence has shown that Omicron may be less likely to result in severe illness or hospitalization, particularly for people who are fully vaccinated.

However, the rapid spread of Omicron has raised concerns about its potential to impact hospital capacity and staffing.

First detected in South Africa in November 2021, the Omicron variant has now become the dominant strain in a number of countries, .

The researchers studied the sensitivity of Omicron to monoclonal antibodies, used in clinical practice to prevent severe disease in people at risk, as well as antibodies in the blood of individuals who were vaccinated or previously infected with SARS-CoV-2, the virus that causes COVID-19.

As part of the research, the Omicron variant was isolated from the nasal sample of a 32-year-old woman, who developed moderate COVID-19 symptoms a few days after returning from Egypt.

The researchers then tested nine monoclonal antibodies used in clinical practice or in pre-clinical development. Six lost all anti-viral activity, they say, while the other three were between three and 80 times less effective against Omicron compared to Delta.

The researchers also cited specific antibodies, some being combinations, including Bamlanivimab/Etesevimab, Casirivimab/Imdevimab and Regdanvimab, which had no anti-viral effect against Omicron, while Tixagevimab/Cilgavimab combination was 80 times less effective compared to Delta.

Some of these antibodies have been approved for use in Canada.

"We demonstrated that this highly transmissible variant has acquired significant resistance to antibodies," Schwartz said.

"Most of the therapeutic monoclonal antibodies currently available against SARS-CoV-2 are inactive."

Looking at the blood of those who received two doses of the Pfizer-BioNTech or AstraZeneca vaccines five months after vaccination, as well as those who were previously infected within the past 12 months, the researchers say the antibodies produced "barely neutralized the Omicron variant," although a booster dose of Pfizer remained effective one month after being administered.