The body then produces that protein and may produce an immune response against it but the method can cause problems.
Sputnik V's makers say the vaccine induced a "strong antibody and cellular immune response," in trial volunteers, according to the official website for the vaccine.
"Not a single participant of the current clinical trials got infected with Covid-19 after being administered with the vaccine," the statement adds.
"It's not clear how efficacious the Russian vaccine is going to be and whether or not people have some prior immunity to the adenovirus that they're using to deliver the coronavirus gene sequence," Gottlieb told CNN Tuesday.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, expressed similar concerns.
"I hope that the Russians have actually, definitively proven that the vaccine is safe and effective. I seriously doubt that they've done that," Fauci told Deborah Roberts of ABC News for a National Geographic event to broadcast Thursday. A portion of the interview was posted by National Geographic on Tuesday.
How did Russia pull this off so quickly?
In April, Russia enacted a law which eliminated the need for a Phase 3 vaccine trial before approval.
Approval now means the coronavirus vaccine can be distributed even as Phase 3 tests get underway -- though practically speaking, mass-manufactured doses aren't expected to be ready for weeks.
"They're not as far ahead as other vaccines," Neal said, noting that Moderna and Oxford's vaccines have already begun Phase 3 trials.
Critics say Russia's haste is partly due to political pressure from the Kremlin, which is keen to portray the country as a global scientific force.
Russia is not alone when it comes to fast tracking -- China approved an experimental coronavirus vaccine in June for members of its military.
And while its vaccine data from Phase 1 and 2 trials are yet to be published, US, UK and Canadian security officials warned in July that Russian cyber actors were targeting organizations involved in coronavirus vaccine development.
Who will get it first?
Russia's Health Ministry has said the country's frontline medical staff and teachers will be the first vaccinated.
The country plans to begin mass vaccination of citizens in October, Kirill Dmitriev, CEO of the RDIF told CNN on Tuesday.
"We will start massive vaccination of Russians in October. This vaccine will be available to other countries around November," Dmitriev told CNN's Anderson Cooper and Dr. Sanjay Gupta.
At the end of July officials denied reports that members of the country's political and business elite -- including Putin -- had been given early access to the vaccine.
Russia plans to mass produce the vaccine by September 2020.
Which countries will take the vaccine? And which won't?
A lot of countries appear keen to try Sputnik V. Dmitriev said at a Tuesday press conference that Russia had "received preliminary applications for over 1 billion doses of the vaccine from 20 countries."
"Countries in Latin America, the Middle East and Asia have displayed the greatest interest in the vaccine, and we are about to finalize a number of contracts for the purchase of the vaccine," he added.
Philippines President Rodrigo Duterte has publicly expressed his enthusiasm for the vaccine and claimed that he is willing to volunteer in further trials.
"I will volunteer to receive it in public. I will be the first to be experimented on," Duterte said during his address to the Philippines late Monday broadcast by state-run RTVM.
As it stands, the Russian vaccine is unlikely to be meet approval regulations for European Union countries and in the US, will need the FDA's approval.
"The US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) have fast-track approval procedures for emergency humanitarian use and we need to see evidence that Russia is adopting an equally prudent approach," said Duncan Matthews, Professor of IP Law at Queen Mary University of London, in a statement to the Science Media Center.
"The point is not to be first with a vaccine. The point is to have a vaccine that is safe and effective for the American people and the people of the world," US Health and Human Services Secretary Alex Azar said on ABC Tuesday. / CNN.com