I'm imagining that a group of humans was transported to a different planet almost 100 thousand years ago.
The planet is similar enough to Earth that they can survive, and already had other earth-based life forms living on it which had arrived there many millions of years ago, but nothing comparable to the level of human intelligence.
Any traits you associate with vampires are cool as long as you can explain them.
Vampires are vulnerable to light and are pale skinned
This planet (or the area the vampires live in) could be hot. Maybe it is slightly closer to the sun or it has greater concentrations of carbon dioxide or other greenhouse gases. This makes daytime too hot for most creatures to be active so they are primarily nocturnal. This forces vampires to become nocturnal for hunting etc. other time they begin to produce less and less melanin. Couple this with a low vitamin D diet and vampires will become very pale skinned in order to get the maximum vitamin D at dawn/dusk to make up for the lack during the day. This would give them no tanning ability so they would burn instantly on direct sunlight.
Vampires are stronger/faster than humans
If the vampires maintain a tribal hunter/gatherer society then they will be more athletic than most humans. This advantage could be increased to supernatural levels by giving their planet slightly higher gravity. This would mean the vampires are used to jumping and running being harder than it is on Earth so they would find jumping on Earth, lifting in our gravity and (possibly) running easy.
Vampires can see at night
Earlier we made vampires nocturnal. If we increase the number of rod cells in vampires. Some humans do have increased rod cells and in nocturnal humans more rods would be an advantage. This would let them see in lower light conditions, probably by moonlight. It would also leave them blinded by too high light levels.
Vampires drink blood If the world they live on is a hot, fairly dry place then prey will be scarce. The vampires need to maximise what benefits they get from prey so will drink the blood to avoid wasting it. Furthermore if the diet is low in iron then drinking the blood of an animal/other vampire/human could be how they counter that.
One of the peculiar traits of vampires is that they are photophobic.
The group of deported humans carried the genes for Porphyria.
Two distinct patterns of skin disease are seen in porphyria:
1) Immediate photosensitivity. [...] Following a variable period of sun exposure—typically about 30 minutes—patients complain of severe pain, burning, and discomfort in exposed areas. Typically, the effects are not visible, though occasionally there may be some redness and swelling of the skin. [...]
Due to the founder effect, the resulting population will carry the same genes and will have to live secluded from daylight, resulting in them being nicely similar to vampires.
If I were attempting to explain it, I would start with how humans got to the planet in the first place. Given that most habitable planets are very far away, the humans travelling from one place to another would either need to have children in space, learn to travel very quickly or find a way to live much longer. The latter is where you can derive long life from by mentioning the science behind telomeres (which degrade as we age to the point of death), telomeres are sections of your DNA that protect all the important stuff, scientists have suggested that finding a way to halt or reverse the degradation of telomeres may hold the key to aging (at least in part).
Related reading: https://www.tasciences.com/what-is-a-telomere/
Once you have the long life as a result of youth you can then go further into the concept of DNA manipulation for space travel, talking about how muscles degrade in space, a solution to this could be to alter the DNA so that the muscle cells are more resistant to low gravity or even completely gravity independent. This would in turn mean that any landing space travellers would have a greater level of strength in comparison to the average human since most of your muscle mass comes from earths gravity and your need to resist it.
Related reading: https://www.nasa.gov/mission_pages/station/research/experiments/245.html
Now that we have established long life and great strength, you need a reason for the vampire population to require extra sustenance, you could justify this by creating a reason why the DNA treatment your humans received for space travel leaves their cells unstable, for example the muscle cells could require hormones or some other chemical to keep them afloat. If we go with hormones for the sake of an example, you could have one of the initial settlers developing a hormone deficiency, requiring that they take the hormones from another by drinking blood etc, but once they drink the other settlers blood, the disease causing the hormone deficiency leads to the bitten settler developing the same deficiency.
The latter is quite sci-fi and will need some imaginative explanation but it's doable, in this example the long life could prevent dying completely (see: http://news.nationalgeographic.com/news/2009/01/090130-immortal-jellyfish-swarm.html), the muscular degradation due to a chemical deficiency would mean that drinking blood heightens strenght and not drinking it reduces strength to little more than an infant (see: http://www.nhs.uk/Conditions/Muscular-dystrophy/Pages/symptoms.aspx) and you could throw in explanations for multiple other abilities.
Other ability explanations include:
All of your vampires could have no idea why they are what they are, a hundred generations down the line from their space exploring ancestors they may have no concept of DNA modification etc. All of these traits could be developed naturally too, in the same way that the Turritopsis dohrnii developed its own immortality in nature, and the same way that plants developed their ability to digest sunlight.
I hope this helps!
