This really depends on how quickly the virus in question mutates and what components of the virus the vaccine keys on for its protective features. HIV evolves q

This really depends on how quickly the virus in question mutates and what components of the virus the vaccine keys on for its protective features. HIV evolves quickly (it is a sloppy replicator and is a fast reproducer) but if the vaccine targets a pathway that all variants use it can end up being effective for a very long time, particularly if the pathway that the vaccine targets is one that is important in how the virus interacts with (or targets in the case of HIV) the immune system.