The study, which has yet to be peer-reviewed, also found the decrease was less pronounced for vaccinated individuals who were previously infected with the virus.
The omicron variant has raised concerns regarding its ability to evade protection provided by widely-used vaccines, with drugmakers tailoring their shots to target the variant while testing the effectiveness of their existing shots.
Vaccines from Moderna, AstraZeneca and Pfizer and partner BioNTech were found to still be active against omicron, but the antibody response was greatly reduced when compared with the original virus strain first detected in China, according to the study.
The Gamaleya Research Institute of Epidemiology and Microbiology in Russia responded to the study.
“A recently published small study addresses Sputnik vaccine’s efficacy against omicron variant deliberately using serum samples that are not representative," the company said. "For example, this study used Sputnik samples with a lower virus neutralization ability against SARS-COV-2 than AstraZeneca’s vaccine while a much larger study in Argentina based on representative serum samples demonstrated 1.8 times higher virus neutralizing titers against SARS-COV-2 for Sputnik, which is explained by its heterologous boosting advantage."
They added: "Therefore, conclusions about Sputnik efficacy against omicron based on wrong serum samples, cannot be made."
The institute said within the next seven days it plans to publish its own data on the topic.
The omicron variant is highly contagious and has more than 30 mutations of the coronavirus spike proteins, which cover the outside of the virus and are the main targets of vaccines and treatments like monoclonal antibodies.
The World Health Organization has said that the omicron variant is spreading faster than any previously detected strain of the coronavirus.
While the omicron variant has been a concern for scientists, the evidence so far shows that it may cause less severe illness than the delta variant.
On Thursday, President Joe Biden warned of a “winter of severe illness and death” for those who are not yet vaccinated against Covid-19 amid a surge in delta infections and as omicron spreads.
Biden made the comments following a briefing on the pandemic with advisers, with the president warning omicron is “now spreading and it’s going to increase.”
The president had said the “good news” was that “if you’re vaccinated and you had your booster shot, you’re protected from severe illness and death.”