MOSCOW — 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.