During the transition from human to Vampire an individual undergoes neurophysical, anatomical and genetic transformations. A person who comes out of a Vampiric coma fully transformed will have undergone a number of major physiological changes affecting the various systems of the body.
A Vampire's nervous system is similar to humans and has proven to be their "achilles heel." Injuries to the spinal cord and brain can be devastating for Vampires. While a Vampire's spinal cord and nerves work as before transformation, a number of changes take place in the brain, and that altered brain chemistry goes a long way toward understanding Vampire behavior.
Vampires have much lower levels of the neurotransmitter serotonin. In humans, low levels of serotonin trigger aggression and risky behavior. A study of murderers on death row revealed low levels of serotonin in their brains. Another neurotransmitter, dopamine induces feelings of well-being. In Vampires, it is released during feeding and has a narcotic-like effect. Circadian rhythms chemical changes in the brain that help us "rise and shine" with the morning light are reversed in Vampires.
Powerful sense organs gives Vampires an advantage both in hunting and eluding capture. Sneaking up on them is virtually impossible, as they are aware of your presence long before you are aware of theirs. In Vampires, the iris in each eye becomes hyperdilated, giving them what appear to be black eyes. While this iris dilation gives Vampires excellent night vision, it renders them effectively blind in daylight. In addition, Vampires suffer inflammation of the sclera, making the whites of their eyes appear red. Smelling and hearing are extremely acute, as Vampires have double the receptor cells in their noses and ears compared to humans. In fact, Vampires usually smell or hear a person coming long before they see one.
During Vampiric coma, the upper and lower canine teeth experience growth. Additional enamel is deposited on the crown of those teeth, turning them into sharp fangs. This is a result of genetic atavism brought on by the HVV's genetic modifications. Vampire fingernails thicken and grow at a rapid rate. A newly-transformed Vampire has a sickly, pale skin tone that turns to a blueish hue over the next few days.
The most profound differences between humans and Vampires are found in the circulatory system. These differences enable Vampires to survive massive trauma that would kill a human being. Vampire blood is pumped via the contraction of skeletal muscle rather than the heart, which eventually atrophies from disuse. Adrenaline, the "emergency hormone," which normally kicks in during "fight or flight" situations, is found in consistently large amounts in Vampire blood. The presence of adrenaline, along with changes in muscle, bone and connective tissue, account for Vampire's extraordinary strength, speed and aggressiveness.
A Vampire's core body temperature is only about 60 degrees, compared to over 98 degrees for humans. This marked difference proved to be a great help for modern vampire fighters, as it made Vampires easily distinguishable from humans when viewed through heat-sensitive infrared imagery.
Adaptations in their skeletal and muscular systems give Vampires significant advantages over humans. About 90% of Vampire muscles are of the fast-twitch variety (compared to 50% for the average human). Fast-twitch muscles enable short bursts of maximal force, ideal when hunting prey. Also, Vampire ligaments and tendons thicken in response to the workload imposed upon them by the muscles. Vampire bones thicken, an adaptation necessary to support their newly-powerful muscles.