MOSCOW (AP) — Thousands of doctors, teachers and others in high-risk groups have signed up for COVID-19 vaccinations in Moscow starting Saturday, a precursor to a sweeping Russia-wide immunization effort.

The vaccinations come three days after President Vladimir Putin ordered the launch of a “large-scale” COVID-19 immunization campaign even though a Russian-designed vaccine has yet to complete the advanced studies needed to ensure its effectiveness and safety in line with established scientific protocols.

The Russian leader said Wednesday that more than 2 million doses of the Sputnik V jab will be available in the next few days, allowing authorities to offer jabs to medical workers and teachers across the country starting late next week.

Moscow, which currently accounts for about a quarter of the country’s new daily infections, moved ahead of the curve, opening 70 vaccination facilities on Saturday. Doctors, teachers and municipal workers were invited to book a time to receive a jab, and Moscow Mayor Sergei Sobyanin said that about 5,000 signed up in a few hours after the system began operating on Friday.

Russia boasted that Sputnik V was the world’s “first registered COVID-19 vaccine” after the government gave it regulatory approval in early August. The move drew criticism from international experts, who pointed out that the vaccine had only been tested on several dozen people at the time.

Putin has shrugged off doubts about it, saying in August that one of his daughters was among the early vaccine recipients.

Over the past months, Sputnik V has been offered to medical workers and teachers even as it was still in the middle of advanced trials. Several top officials said they also have received the jabs, and earlier this week the Russian military began vaccinating crews of navy ships scheduled to depart on a mission.

Health Minister Mikhail Murashko said Wednesday that more than 100,000 people in Russia already have received the shots.

The free vaccine is offered to people aged 18 to 60 who don’t suffer from chronic illnesses and aren’t pregnant or breastfeeding.

The two-shot Sputnik V was developed by the Moscow-based Gamaleya Institute. An advanced study among 40,000 volunteers was announced two weeks after the vaccine received government approval and that is still ongoing.

Last month, developers of the vaccine said interim analysis of trial data showed it was 91.4% effective. The conclusion was based on 39 infections among 18,794 study participants that received both doses of either the vaccine or a placebo, which is a much lower number of infections than Western drugmakers have looked at when assessing the effectiveness of their vaccines. Two other Russia-designed vaccines are also undergoing tests.

On Wednesday, Britain became the first country in the West to authorize the use of a vaccine against the coronavirus developed by U.S. drugmaker Pfizer and Germany’s BioNTech.

Russia has been swept with a resurgence of the outbreak this fall, with numbers of new infections exceeding the levels recorded early in the pandemic, but the authorities so far have refrained from a tight lockdown imposed in the spring.

On Saturday, Russia reported a new record high of daily infections at 28,782, including 7,993 in Moscow. The government task force has recorded a total of 42,684 virus-related deaths since the start of the outbreak.

Russia’s total of over 2.4 million confirmed cases is currently the fourth-largest caseload in the world behind the United States, India and Brazil.