The Vampire Status (also known as Vamp or Vampirism) is a status effect that appears in Castlevania (N64) and Castlevania: Legacy of Darkness. Throughout the game there are enemy vampires who will attempt to sink their fangs into the hero's neck. If one is to successfully bite the player during their quest, and he/she is not able to shake it off in time, then the status of the player will change from "Good" to "Vamp".
Aside from the hideous greyish skin color that comes with it, the Vampire status has many other negative effects to it that players need to watch out for. The first noticeable effect is that the main attack becomes disabled, leaving only the seldom short-ranged alternate attack available for use in combat (excluding sub-weapon attacks). Cornell also gets an additional feature where he won't be able to use his Werewolf form (however, Cornell is immune to the infection whenever he has transformed into a Werewolf).
The second noticeable effect is that using Roast Chickens or Roast Beefs to restore lost HP becomes impossible. Finally, the last effect that isn't noticeable until it's too late, is that if the player remains in this state for too long without getting it cured, then they'll submit to the urges of being a vampire (video), and at that point, the game ends in evil's favor.
The point when they submit to the urge is always at the stroke of midnight (00:00) in game time. However, if the player is infected an hour before midnight, then they're given an extra day before their wills give out. For example, if the hero was infected at exactly 23:00, then they'd still have an extra day left to try and cure it. But, if the hero was to be infected at exactly 22:59, then unless an item capable of curing the affliction or delaying its effects was already in possession, they are most likely doomed to failure, as the hero would only have roughly one hour (in game time). The player can prolong the time they have left by the use of Sun and Moon Cards, since the in-game clock does pause and they cannot die or get hurt by anything while in the main menu. Regardless, it's best to treat this status as soon as possible.