Sputnik V vaccine's official website claims that their product is the first registered against the disease.
Sputnik V is the world’s first registered vaccine based on a well-studied human adenoviral vector-based platform.
Skeptics Stack Exchange is a question and answer site for scientific skepticism. It only takes a minute to sign up.Sign up to join this community
It is indeed the first registered vaccine. But the registration process in Russia is different than in other countries (say, USA). They basically skipped the third stage: testing the vaccine on a large number of humans. So the vaccination which is happening in Russia can be viewed as the third phase of testing. Thus even though it was registered first, it could not be viewed as thoroughly tested, at least till a few days ago.