The COVID-19 vaccine developed by the Gamaleya Research Institute of Epidemiology and Microbiology is called "Спутник V". Per the English-language Wikipedia page, the "V" is the letter "V", not the Roman numeral five. Apparently, even the original cyrillic spelling is "Спутник V", although "V" is not a letter of the cyrillic alphabet. I would rather have expected "Спутник В" (capital "в" for "вакцина").
Why was a non-cyrillic letter used even in the original cyrillic name of the vaccine? Was this exclusively driven by marketing, for fear of the rest of the world mistaking a "в" for a (roman) "B"?
Is there a general rule in Russian about using Cyrillic or Latin letters for one letter brand or class names?