@depzdai - in most stories about vampires, they have access to blood packs too. Even when they are a secret. Imagine a vampire cabal sponsoring blood donation campaigns.
Also, vampires mostly drink AB+ blood, the "universal recipient" kind. It can only be given to other people with AB+ blood. When news say somebody has trouble getting blood, it's because they have a rare blood type like O-, which doesn't allow them to take blood from people with any other blood type.