Russia claims to have spotted another type of Covid that could thwart the power of vaccines, it was revealed today.
Scientists are now scrambling to find out whether jabs still work against the mutant 'Moscow' strain.
Health chiefs have not released any public detail about the variant and local media says experts are confident vaccines should still be effective.
Moscow's coronavirus outbreak has been growing since mid-May, with 7,704 cases reported across the city on Sunday — the most in a single day since December 24.
Academics at the Gamaleya Research Institute of Epidemiology and Microbiology, which produces the Sputnik V vaccine, suggested the new variant could be blame for the rocketing numbers.
Deputy director Denis Logunov told the state-owned Russian news agency TASS: 'Now we are monitoring [the situation] in Moscow, and most importantly, Moscow may still have its own Moscow strains.'
Mayor Sergei Sobyanin said on Saturday the city was repurposing thousands of hospital beds for an influx of Covid patients and told residents to stay off work in the coming week to help curb the spread of the virus.
Sports pitches, playgrounds and other attractions inside large parks were closed for a week from Sunday. Bars and restaurants were ordered to close no later than 11pm.
Scientists are now scrambling to find out whether jabs still work against the mutant 'Moscow' strain. Mocked-up image of a coronavirus
What are the main variants recognised by the WHO?
First spotted: Kent
First spotted: South Africa
Scientific name: B.1.351
First spotted: India
Scientific name: P.1
First spotted: India
Mr Sobyanin said: 'This is only a temporary solution.
'To avoid new restrictions and secure a sustainable improvement of the situation, we need to significantly speed up vaccinations.'
Gamaleya Institute head Alexander Gintsburg said he believes the strain is not resistant to jabs.
Mr Gintsburg told the Moscow Times: 'We think that the vaccine will be effective, but we must wait for the study results.'
Coronaviruses — including the type that causes Covid — are constantly evolving to become better at spreading.
Several different Covid variants have already emerged since the pandemic began, including the Kent 'Alpha' variant, which quickly became the world's dominant strain.
Scientists at Britain’s Covid-19 Genomics UK Consortium (COG-UK) first detected the B.1.1.7 variant of coronavirus in September in the English county of Kent.
It took almost three months before they discovered that the variant was 70 per cent more transmissible than existing variants and further weeks before discovering it was also much deadlier.
The coronavirus has undergone thousands of mutations since its emergence in 2019, but most make no difference to its impact on human health.
But B.1.1.7 drove a surge in cases that flooded Britain’s hospitals, pushed its death toll above 125,000, and triggered travel bans by dozens of countries.
The South Africa 'Beta' variant is thought to be partially resistant to vaccines but its lower transmissibility means it has become dominant in the UK or abroad.
Now the Indian 'Delta' variant has taken over in the UK and scuppered lockdown easing plans because it is 60 per cent more transmissible than the Kent variety, according to experts.
But the vaccines are thought to be as effective against the strain after two doses, with two separate Public Health England studies showing that having both jabs is as effective at producing deaths and hospitalisations for the variant as they are for the Kent one.
Russia's controversial Covid jab is 92% effective: 'Sputnik V' vaccine which Vladimir Putin is safe and prevents almost all deaths and hospital admissions, major trial finds
Russia's controversial coronavirus vaccine is 92 per cent effective at blocking symptomatic illness, trial results suggest.
Just 16 out of 16,500 people given the two-dose jab – dubbed Sputnik V – developed symptoms, while no-one died from the disease or needed hospital treatment.
In a huge boost to Russia's immunisation ambitions, the vaccine was also found to be 74 per cent effective at blocking Covid after just a single dose.
For comparison, AstraZeneca's vaccine is roughly 70 per cent effective at blocking symptomatic Covid after two doses, while the efficacy for jabs by Pfizer and Moderna is around 95 per cent. But directly comparing results from trials done in different countries is difficult because trial methods and standards vary.
Sputnik V, named after the former Soviet space satellites, has been shrouded in controversy since Vladimir Putin green-lit its approval for mass-use in Russia last August before any human trials had been rigorously analysed. But the jab has still not actually been rolled out nationwide.
Top UK scientists and politicians denounced the move because there was no evidence to prove the vaccine worked or was safe and accused Putin of trying to elevate Russia's international standing.
The following month British spies accused the Kremlin of launching a cyber attack on Oxford University scientists who developed an almost identical vaccine, raising fears Moscow was stealing research from the UK.