The developers of Russia's Sputnik V coronavirus vaccine on Tuesday criticised Brazil's refusal to import the jab as politically motivated.
Brazilian health regulator Anvisa on Monday denied requests from several states to receive batches of Sputnik V, saying it did not have the data needed to verify the jab's safety and efficacy.
The Brazilian regulator gave the green light to two Covid-19 vaccines -– AstraZeneca and Coronavac – in January, and has also approved both Pfizer-BioNTech and Johnson & Johnson's shots, which have yet to arrive in the country.
"Anvisa's delays in approving Sputnik V are unfortunately of a political nature and have nothing to do with access to information or science," the official Sputnik V Twitter account said.
It pointed to a recent US government report that said Washington had tried to persuade Brazil not to use Sputnik.
"The United States Department of Health, in its 2020 annual report several months ago, publicly stated that the United States health attaché 'persuaded Brazil to reject the Russian vaccine against Covid-19,'" the account added.
Anvisa said its experts had flagged "uncertainties" about the jab, which has not yet been approved by the European Medicines Agency (EMA) or the US Food and Drug Administration (FDA).
"We will never allow millions of Brazilians to be exposed to products without due verification of quality, safety and efficacy, or at minimum, facing the grave situation we are now going through, that the benefits will outweigh the risks," said Antonio Barra Torres, president of federal health regulator Anvisa.
Anvisa, which received a request last month for emergency use of the Russian formula, has not released its findings, or cited the specific information it determined was lacking.
The Russian vaccine has so far been approved for use in at least 60 countries, including more than 10 in Latin and Central America.
Argentina signed a deal with Russia earlier this month to become the first Latin American country to produce Sputnik V shots, and will aim for full-scale production to start in June.
The Kremlin said Tuesday it needed more information about the Brazilian decision before commenting, adding that it was not in touch with Brazilian authorities on the issue.
But in general, Kremlin spokesman Dmitry Peskov told reporters: "We are against the use of vaccines as a political tool."
Some Western countries have been wary of Sputnik V – named after the Soviet-era satellite – over concerns the Kremlin would use it as a soft power tool to advance its interests.
Moscow registered the jab in August before large-scale clinical trials, but leading medical journal The Lancet has since said it is safe and more than 90 percent effective.
Experts at Anvisa said the medical journal's study had a different scrutiny process from the regulatory body.
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"A journal does not have the same objectives of determining whether or not to approve the use of a vaccine," said Gustavo Mendes, one of Anvisa's technical managers.
Brazil has recorded more than 390,000 Covid-19 deaths, the second-highest number globally, behind only the US. But the government has struggled to secure enough vaccine doses for the country's 212 million people.
So far, it has managed to administer over 38 million vaccine doses.
But the country's outbreak, which has sickened more than 14.3 million people, has continued to surge, pushing hospitals to the breaking point.