MOSCOW – Russia on Tuesday became the first country to approve a coronavirus vaccine, a move that was met with international skepticism and unease because the shots have only been studied in dozens of people.

President Vladimir Putin, who announced the Health Ministry's approval, said one of his two adult daughters was already inoculated. He said the vaccine underwent the necessary tests and was shown to provide lasting immunity, although Russian authorities have offered no proof to back up claims of safety or effectiveness.

"I know it has proved efficient and forms a stable immunity," Putin said. "We must be grateful to those who made that first step very important for our country and the entire world."

However, scientists in Russia and other countries sounded an alarm, saying that rushing to offer the vaccine before final-stage testing could backfire. What's called a Phase 3 trial — which involves tens of thousands of people and can take months — is the only way to prove whether an experimental vaccine is safe and really works.

By comparison, vaccines entering final-stage testing in the U.S. require studies of 30,000 people each. Two vaccine candidates have already begun those studies, with three more set to start this fall.

"Fast-tracked approval will not make Russia the leader in the race, it will just expose consumers of the vaccine to unnecessary danger," said Russia's Association of Clinical Trials Organizations, in urging government officials to postpone approving the vaccine without completed advanced trials.

While Russian officials have said large-scale production of the vaccine wasn't scheduled until September, Deputy Prime Minister Tatyana Golikova said the vaccination of doctors could start as early as this month. Officials say they will be closely monitored after the injections. Mass vaccination may begin as early as October.

"We expect tens of thousands of volunteers to be vaccinated within the next months," said Kirill Dmitriev, chief executive of the Russian Direct Investment Fund, which bankrolled the vaccine.

The vaccine developed by the Gamaleya Institute in Moscow with assistance from Russia's Defense Ministry uses a different virus — the common cold-causing adenovirus — that's been modified to carry genes for the "spike" protein that coats the coronavirus, as a way to prime the body to recognize the real COVID-19.

That's similar to technology in vaccines being developed by China's CanSino Biologics and Britain's Oxford University and AstraZeneca — but unlike those companies, Russian scientists haven't published any scientific information about how the vaccine has performed in animal tests or in early-stage human studies.

Dmitriev said advanced trials are set to start Wednesday that will involve "several thousand people" and span several countries, including the United Arab Emirates, Saudi Arabia, the Philippines and possibly Brazil.

The Associated Press couldn't find documentation in the Russian Health Ministry's records indicating that permission to start the advanced trials was granted.