MOSCOW– Russia's Sputnik V vaccine against COVID-19 is around 83 percent effective against the Delta variant, lower than previously thought, Health Minister Mikhail Murashko said on Wednesday.

Authorities blamed a surge in coronavirus cases in June and July on the more contagious Delta variant and the population's reluctance to get vaccinated despite shots being widely available.

The vaccine's developers in June said Sputnik V was around 90 percent effective against the Delta variant.

"The latest results show that effectiveness is around 83 percent," the TASS news agency cited Murashko as saying.

• Moscow begins booster vaccine campaign as Russia's COVID-19 cases surge

Alexander Gintsburg, director of the Gamaleya Institute which developed the vaccine, said on Wednesday in an interview with the Izvestia newspaper that Sputnik V was safe and effective against all strains of the coronavirus.

Russia, which has a population of around 144 million, has approved 4 domestically produced vaccines. It has recorded almost 6.5 million infections since the start of the pandemic.

• Global COVID-19 cases top 200 million as Delta variant rages

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