Russia’s Sputnik V provides the best protection against the Omicron variant of the coronavirus, its developers said Friday, disputing a Western study which found the COVID-19 vaccine produced no antibodies against the latest variant of concern. The Gamaleya Institute and the Russian Direct Investment Fund said in a statement that a preliminary laboratory study showed Sputnik V had “the best virus neutralization results against omicron in comparison with other vaccines.” Russian President Vladimir Putin also praised Sputnik V efficiency against Omicron earlier Friday.

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“Our Sputnik V is working well, and, perhaps, even more effective against the omicron than other vaccines used,” the president said during a congress of the Russian Union of Industrialists and Entrepreneurs.

International researchers from the University of Washington and the Swiss drugmaker Humabs Biomed SA said in a study published Tuesday in pre-print and yet to be peer-reviewed that data they analyzed showed conflicting results.

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The study, which used samples from health care workers in Buenos Aires, Argentina, who received Sputnik V, showed “no neutralising activity against omicron.”

Russia has so far reported 25 cases of the omicron variant in the country, according to Deputy Prime Minister Tatiana Golikova.

The World Health Organization (WHO) this week warned that Omicron was spreading at a rate not seen with previous strains.

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“Seventy-seven countries have now reported cases of Omicron, and the reality is that Omicron is probably in most countries, even if it hasn’t been detected yet,” WHO chief Tedros Adhanom Ghebreyesus told reporters during a media briefing in Geneva on Tuesday.

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Omicron was first detected in South Africa in November, and flagged by the WHO as a variant of concern due to its high number of mutations, which make it potentially more transmissible and elusive to immunity provided by previous COVID-19 infections or vaccines. UK Prime Minister Boris Johnson cautioned against the notion of Omicron being a “milder variant”as the country Wednesday recorded its highest number of daily infections since the start of the pandemic.