Russia has admitted that it misunderstood the requirements for its Sputnik V coronavirus vaccine to be approved for international use.
The Kremlin acknowledged on Tuesday that Russia failed to meet the requests of the World Health Organization (WHO).
Russia was the first country to approve a COVID-19 vaccine for use in August 2020, developing their Sputnik V jab.
The Lancet medical journal has said the vaccine has an efficacy rate of 91.6% against COVID-19, and SputnIK V has since been rolled out by several countries.
But over a year after its launch, the vaccine has still not been approved by the WHO or the European Medicines Agency (EMA).
In September, a regional WHO official said the manufacturing process of the Sputnik V jab had not met the necessary standards.
Kremlin spokesperson Dimitry Peskov said that Russia had struggled to provide documentation to certify its vaccines with the WHO.
"We have not yet provided some of the information that should be provided because we had a different understanding," Dmitry Peskov told reporters in Moscow.
"We have different standards," he said, adding that Russia was "gradually adapting to these demands".
The Kremlin has also said that Russian authorities had nothing to criticise themselves for.
Russian authorities have said that distrust in Sputnik V -- as well as other Russian COVID vaccines -- has contributed to the country's low vaccination rate.
According to the Gogov website's baseline count, just 42.2% of the Russian adult population is fully vaccinated against the virus. Meanwhile, the country has registered more than 10 million cases of COVID-19 since the start of the pandemic.
The national statistics agency Rosstat has estimated that more than 520,000 have died of infection, significantly more than official figures.
In response to the Kremlin, the Anti-Corruption Foundation (FBK) of Russia's opposition leader Alexei Navalny mocked the failure to get Sputnik V approved.
"Somehow other vaccine manufacturers have managed to understand what the WHO requires of them for certification, and only ours 'don't understand'," the FBK said on Twitter.
"As a result, our own citizens don't trust the vaccine because it can't be approved by the WHO," it added.
"People are dying and they are [still] going through the paperwork."