An Aerolineas Argentinas plane left Buenos Aires for Russia late Tuesday on a trip to pick up a third batch of Sputnik V coronavirus vaccines after the flight was delayed from its originally scheduled departure Sunday.
"Today, at 9 pm, the third @Aerolineas_AR flight took off for Moscow to bring new doses of the Sputnik V vaccine to the country," airline president Pablo Ceriani tweeted.
Flight AR1062 is planned as a 40-hour operation in total, he said, calling it an "important logistical effort that requires coordination from different actors in both countries."
The flight was scheduled to depart on Sunday to bring back a third batch of the 19.4 million doses Moscow had committed to provide before the end of February.
So far, Argentina says it has received 600,000 shots of the vaccine that requires two doses.
Airline boss Ceriani tweeted on Monday that the flight would be rescheduled "as soon as we have a confirmation from all the parties involved in the supply chain."
The government gave no reason for the delay.
Aerolineas Argentinas has already sent two flights to Russia to bring doses of the vaccine which health officials started administering on December 29.
The country of 44 million inhabitants has recorded 1.8 million coronavirus infections and 47,000 deaths.
President Alberto Fernandez and Vice President Cristina Kirchner have both been vaccinated, and the next vaccination priority group is set to include seniors over age 60.
It is administering the second vaccine dose to health personnel in the initial stage of a national inoculation program.
The Fernandez administration says it has secured more than 51 million vaccine doses.
Including its deal with Russia's Gamaleya laboratory, Argentina has signed contracts for the delivery of the shot developed by AstraZeneca and Oxford University, is negotiating with drug maker Pfizer for access to its vaccine, and will also get doses under the UN's Covax distribution project.
Sputnik V is still undergoing Phase 3 trails, the final testing round before a drug is approved.
Russia says the shot has been given to some 1.5 million people, and early trial results have shown it to be more than 90 percent effective.
Europe, too, is having trouble getting promised vaccine deliveries as drug makers struggle to keep up with demand.