The vaccine was well-tolerated and worked in the elderly as well, according to the peer-reviewed findings, which were published Tuesday in the medical journal The Lancet. Sputnik V showed efficacy of 91.6%, validating claims by the developers last year.

The findings buoy the vaccine’s credibility after it faced accusations of being rushed to market before critical scientific data was available. Sputnik V is approved for use in 16 countries, from Argentina to Iran.

“The development of the Sputnik V vaccine has been criticized for unseemly haste,” Ian Jones, a professor of virology at the University of Reading, England, said in an accompanying comment in The Lancet. “But the outcome reported here is clear and the scientific principle of vaccination is demonstrated, which means another vaccine can now join the fight to reduce the incidence of Covid-19.”

Although the results aren’t final, the vaccine joins only a handful of others, including ones developed by Moderna Inc., AstraZeneca Plc and Pfizer Inc. and BioNTech SE, in showing it works in an advanced clinical trial. It differs from the others in that its two doses reply on different viral vectors, which offers it an advantage against new strains, said Kirill Dmitriev, the head of co-developer the Russian Direct Investment Fund.

“We don’t have any doubt that the vaccine will be approved by the World Health Organization,” Dmitriev said in an interview. “It has high efficacy and it is one of the most accessible due to its price and the ease of its logistics and storage.”

The developers last met with the Geneva-based public health organization on Jan. 22 to discuss their application, and no time-frame has been given for approval. The vaccine hasn’t been submitted for review to Western regulators yet.

Initial tests by RDIF’s partner, the Gamaleya Research Institute of Epidemiology and Microbiology, show that the vaccine remains effective against new strains of Covid-19, according to Dmitriev.

South African and U.K. variants of Covid-19 appear to be more transmissible than the original virus and have raised fears that they could impact the effectiveness of existing vaccines or require a booster dose.

Dmitriev said tests of a combination of AstraZeneca and Sputnik V vaccines are scheduled to begin next week, with the first trials in Azerbaijan and the United Arab Emirates. The mix may prove more effective against new strains, he said. RDIF plans to offer its inoculation as a second dose to producers that have vaccines with efficacy below 90%.

Full Protection

The vaccine provided full protection against severe cases of Covid-19, while showing virtually the same efficacy for volunteers over the age of 60, according to the published data. Dmitriev said that researchers are preparing to study its use for children, as well.

The peer-reviewed publication may help Russian efforts to vaccinate 60% of its adult population in the first half of the year after a slow initial roll-out. The homegrown shot has faced doubts at home. Only 38% of Russians are ready to take Sputnik V, according to a Dec. 21-23 poll conducted by the Levada Center.

Many vaccination centers in Moscow, where the campaign is largest, are not working at capacity even after Vladimir Putin ordered universal access to the inoculation in mid-January. The Russian president hasn’t yet said when he’ll get vaccinated.

Sputnik V should provide protection against Covid-19 for over a year, and can be employed again for re-vaccination, according to Dmitriev. He said he took a booster shot seven months after his first to test his cellular immune response, which produced antibodies faster than after his initial vaccination.