What would be the minimum human population to sustain a single vampire indefinitely?

As per question in the title.

I recognise that there are numerous criteria that would affect this, however, I am looking for a baseline estimate that could be modified as per specific vampire (his humanity, feeding habits, discipline usage etc.) I would assume that the said vampire is drinking about 2-3 points of blood per night and never kills his victim. However, I struggle to estimate anything else than a herd size (which is composed of exclusively fit-for-purpose healthy people). Assuming that it takes about four months to recover from a loss of a point of blood without any detrimental health effects (implied by the facts that a point is about a pint, that is about a single blood donation and the medical recommendation is to donate blood at most three times a year), I propose the following calculation:

3 * 1 * 4 * 31 = 372 people required to every night feed on 3 different people, drawing 1 point of blood for four months of 31 days, so that no person is bitten twice in this period.

But that doesn't explain how many "real" people would be necessary to at all times have no less than 372 healthy specimens for an indefinite amount of time (self-sustaining population).

Could you explain how to get that number and what would be the major contributing factors?

If this question is not fit to appear here, I could possibly ask in some medical SE instead. Please comment if that's the case.

Some people ask me for purpose, let me explain. That's not supposed to be a tool to estimate the vampire population in a given city. Instead I'm thinking about a single vampire living in a remote area without a practical possibility of leaving (think Tzimisce in a settlement surrounded by werewolves in the middle of Siberian taiga). I am trying to establish how many people should such a vampire have around him to survive by purely local means. I want to take into consideration aspect like not everyone having being suitable to be fed upon, naturally occurring illnesses, necessity of children to replace the elderly etc. to create a situation where a trapped Cainite struggles to keep himself alive. There are some imminent dangers to him, hence his usage of disciplines (additional 2 points per night) but he is aware that overfeeding would steer the population to a decline. I would like that status quo to last for more than five decades. No, I don't want to factor in the social problems of people gradually noticing his presence, I'd rather think of superstitious community who treats it as a curse over a town that has no explanation and him being extra careful to influence mortals into having a lot of children and not leaving, as a local prince could in the medieval times - only in contemporary setting.

Mortals are not supposed to be willing participants, if it were like that, I'd just go with Herd Background and assume no overhead of spouses, children and elders is needed.

Like many things, it depends. Your calculations are quite reasonable and 372 should give your vampire enough, in fact it has a decent margin of error in it. It has a decent margin of error because a healthy person can give more than 1 BP in a night. I don't have the book handy, but I'm pretty sure they can give up to 3 BP before their life is endangered. Also a healthy person can give blood more often than the medical guidelines indicate. Further, the vampire can, at least to a degree, self regulate and avoid using unnecessary blood. You will still average well above 1BP a night, but a vampire that avoids fights and is deliberately conservative about blood use can probably come in under 2-3 BP a night on average.

So, as you say 372 will provide enough, and even give some safety margin. But that is 372 adults that are at least healthy enough to "contribute" three times a year. You are asking how many would be in a community to give you those 372 healthy adults.

And that depends. You want the birth rate to be equal to or greater than the death rate, but death rates are highly variable in different time periods and different parts of the world depending on circumstances. In the United States, for instances the crude death rate is 8 per 1,000 people per year. Going with that number and ignoring the fact that that is per 1,000 in the entire population and we are only looking at health adults in our 372, he can expect to lose around 3 of his herd each year. That means to be sustainable he needs 3 that are about to become old enough waiting in the wings. If we say they are "adult enough" at 16 and we want this to be indefinite we need 3 children at each age between newborn and 15 waiting around. So, in addition to our 372 adults, we need 48 children waiting around.

Incidentally, the crude birth rate in the US is 14 per 1000 people, so for our 372 adults we could expect an average birth rate (if comparable to US) of 5, easily more than the 3 we need.

Currently, this brings us to 420 to be sustainable. But, you also won't be able to count those with chronic infirmities that prevent them from contributing, like the very elderly. But how many elderly you have also depends. If the death rate is high, you probably won't have many. If you have customs of senicide (killing or suicide of the elders), then again you won't have many. If the vampire has a firm hold and wants to keep the population to a minimum, he might well create such a custom or else "cull" his herd of any not of use to him. If he does this ruthlessly, than 420 is enough with a decent safety margin. But, if he doesn't do this then he will have some additional people. In the US our population over 65 is 13% of total. With a base of 420 people, this makes 483 people total (13% of 483 is 63), so if this is a rough estimate of the number in his population he can't eat than we are up to 483.

I'm ignoring the temporarily sick because (unless there is an epidemic hitting a large percentage of the population) he can easily bypass them for a week and just come back. In short, they are absorbed into the safety margin.

So, I've played rather loose with a lot of the estimates and erred on the side of the vampire being cautious, but a population of 483 could sustain a vampire forever. This of course adds in the assumption that there won't be any huge deviations from average. If there is a war or plague or famine that wipes out a large portion of the population, he will have trouble.

• But a vampire that does not have feeding limitations can suck dry a peasant that is about to die, if nobody will investigate the death (i.e. not in modern times). This can push the amount of people needed down, but your estimate is fine. Commented Aug 10, 2017 at 21:35

The question is somewhat flawed. If the question is really the first premise I list, then a minimum of 80 mortals are required for a sustainable herd population.

• A vampire wishes to have a sustained community of blood dolls, taking 2 points of blood a day
• A mortal adult has a blood pool of 10 (VtM:Rev 139, chart)
• A Kindred can drink 20% of a mortal's blood pool without causing harm (VtM: Rev 139)
• Therefor a Kindred can drink 2 points of blood from a mortal without causing harm
• A mortal refills one blood point a day. (VtM:Rev 140)
• Therefor a mortal could be fed on every other night if the kindred decided to drink 2 points of blood from one mortal a night.
• Therefor a stable herd size for a Kindred who uses two points of blood a night is 2.
• If a kindred decided to drink only one point of blood per mortal per night, they would need exactly as many mortals as blood the desire to drink every night, in this discussion, 2

Either way, a kindred would only need 2 blood dolls to sustain a diet of 2 blood points a night.

Knowing that you only need 2 mortals to sustain a vampire indefinitely, it becomes academic to determine the minimum viable population of humans. Scientists have done the work on that. The article posted in New Scientist in 2002 claims the "Magic Number" of a minimum population is 160, perhaps as few as 80 if the mortals are genetically screened for undesirable recessive traits. This provides far above the required 2 that need to live as blood dolls.

• Since you both have your own answer, rather than arguing in the comments on each other's posts, please focus on improving the case made by your respective answers on the points on which you differ. Commented Nov 22, 2015 at 22:55

Here are my 2 cents.

I considered OP's scenario, but wanted to add a twist to it.
I considered the Vampire does not have to be awake all time and could use some nights of rest if he or she finds a hiding spot that will last for a while. Thus, here is my typology of situations he or she might face, each night:

• CASE A - Night of rest (no blood points spent)
• CASE B - Has to awake to do some chores and incidents make him use disciplines (1 BP for the awakening and between 1 and 2 extra ones)
• CASE C - He is awakened by imminent danger, which makes rises the BP expenses. The overall expense is between 1 and 3 BP each night, as posited by OP. I biased my simulation towards Case C, which is a 50% random event (e.g. Werewolves storming your hideout) and then, out of the remainder 50%, I sorted randomly the other two options.

Note: The BP expense is always between 1 and 3. I could have made it easier, but this Case-driven simulation is the result of a previous arrangement in which I conceived of the possibility of spending 0 BP on some nights of rests, which is clearly denied by @DannnyCuppen, who kindly pointed out the fact p. 268 of the V20 edition says 1 BP is spent daily during slumber, and even twice is there is a daily awakening followed by another session of slumber.

Thus, I believe my simulations should account for the high-tension scenario put forward by OP, while, at the same time, accounting for occasional days of rest or basic chores on the remaining days.

For 100 simulations run over a period of 2 years, the BP expenditure ranges around 1800 BPs... That is, around 900 BP per year.

After doing this, I considered the following:

1. Taking 1 BP from a human equals to about 1 donation
2. Although blood volume is recovered in 24-48 hrs, haemoglobin takes 14 days on average to be recovered
3. Suggested recovery times are 112 days (i.e. 16 weeks -- click here for a UK reference), but may be as short as 56 days for men and 84 days for women (see what WHO says at page 44 -- paragraph 4.6.2)
4. Over 2 years of donation, donors who stick to the shortest time frame might develop iron deficiency... Hence, I freely assumed each donor who is subject to feeding events at a certain ratio must be given a 2 years break every 2 years of donor activity

Another assumption is that each BP requires a feeding event from a separate individual, since OP did not mention the need for our Vampire to cover up his activities.

In my next simulation, I considered how many BPs are needed each day, with a "refill ASAP" logic in mind.
I also accounted for the fact that "donors" become available again after 84 days (men) and 56 days (women) (see above). I also randomised male and female feeding events, so that, for every feeding event, the re-entry point in my feeding pool could vary.

I ran this crude simulation (very crude, actually) 54 times. The resulting feeding pool never exceeded 203 individuals and never went below 185 individuals.

Now, considering my 4-years refresh rate (which is charitable, I know), this means the feeding pool, in the worst case scenario, should always include around 406 individuals. Very similar to OP's estimate of 372.

Let's now move to the population part. I assumed that:

It follows every year 7.4 adults come out of age.
This means (drawing on ideas presented in other responses to this threas) that we need 7.4 new teenagers coming of age each year.

But what about the premature mortality rate of adults in the feeding pool?

My only available data are for the WHO EU region. This region is useful as it includes countries with a great deal of variation (think of comparing Norway with Russia). This should give us the best shot at an estimate.
Now, I only have the following info:

• Age-standardized overall premature mortality in people aged 30-69 years for four major noncommunicable diseases (cardiovascular, cancer, diabetes, chronic respiratory) = 379.62 per 100,000 (Source: WHO)
• Age-standardized mortality rates from all external causes and injuries = 49.93 per 100,000 (Source: WHO)

Although the former of the two datasets considers 30-69 and not 16-69, I am happy to go along with both of them, for sake of simplicity.

The result is 0.0043% premature deaths every year. This means that, every year, we have to replace another 2 adults in our feeding pool.

Possible biases: Premature deaths mean less adults reaching the aforementioned ceiling age (70 y.o.); I did not account for this. Moreover, one could argue that the premature deaths factor in diseases that make someone unsuitable to donate; that is, I should have considered only death from external causes as an agent that drains my feeding pool. If that was the case, with a charitable 49.93 out of 100,000, I could expect as small as 0.0005% of the feeding pool disappear by accident (that is, negligible). Our Vampire, however, is not a doctor and does not diagnose patients (I assume); thus, to play it safe he should consider the possibility of feeding from the wrong people or his feeding pool draining faster than he think.

Therfore, I argue that a good margin of error (in excess) is my combined number of premature deaths for all causes. For a population of 406, this number is 2 per 1,000 people. Hence, considering those who turn elderly, overall yearly replenishing rate of the feeding pool should be of around 9.4 individuals per year (again: to play it safe).

This falls within the birthrate range of the countries with the lowest birthrate in the world (see this chart for an overall perspective).

All data, then, point at a community with:

• Around 1,000 people
• Birthrate of at least 9.4 per 1,000 pop.
• 406 potential donors

We can test this by doing a reverse calculation: considering that suitable donors are estimated to be around 37% of the population (all citizens, including kids) (Source data is from the USA, which is definitely not top notch in terms of overall access to healthcare and overall security). Note: some respondents to this thread mentioned figures as small as 3%. This is wrong, because they are looking at the percentage of people who actually donate, which is a free choice. In our case, the Vampire does not act like the Red Cross, so that our 37% will have little choice and every candidate will be exploited.

If 406 donors are 37% of our overall population, it means that, well... our total population has about 1098 people (including the kids and the elderly). This is very close to our expectations in terms of birthrate and replenishment of our feeding pool!

Final Breakdown

• Total pop.: 1098+
• Feeeding pool (worst case scenario): 406
• Kids in the community (aged 0-15): 151
• Remainder (too weak to donate and/or too old): 541+
• Blood Points needed per year: 933-934 (according to my last simulation)
• Peak individuals out of the feeding pool at any given time (due to short, but not too short recovery window periods): 203 (according to an "awakening-scenarios" simulation that was run 100 times)

Now, this should set OP up for a situation in which overfeeding should be avoided while, at the same time, account for a sufficiently thrilling long-term survival scenario.

Discussion: communities and their demographic history

Some results might have to be adjusted. After all, I used nationwide data, but we all know birth rates vary regionally. An isolated but thriving mining community might have a birth rate that is higher than the rest of the country.
Also, you should factor some history in the picture: how long has the vampire been there for? Human communities thrive and decline and hardly remain stable. If he came to the mining town in the 60s, he might have witnessed a pop. boom, which would have set him up for the next decades. History is a player even if you consider role play set in contemporary eras... A lot of things have changed on Earth since 50 years ago!

Now, talking short-term illnesses, I did not factor them in. It all depends on the type of community you want. Isolated might mean poor access to healthcare, but it might also mean its inhabitants are shielded from pandemics. Another thing I cannot factor in is whether or not the vampire is a disease carrier. In such case, influenza would spread very quickly among people.

Finally, I would like to invite you to consider the possibility of spiking "death rate from other causes" in order to give your dude a 10 BP boost every now and then. In Russia, which has a murder rate of 10 per 100,000 you could afford a vampire-led murder every 10 years. Also, you could feed on people close to the end of their life cycle to avoid taxing your feeding pool. This should give the vampire some occasional boosts.

I hope this answers your questions both demographically and narratively.

P.S.: I would like to thank everyone who helped me edit this. I came back to update sources and calculations. I apologise if my earlier contribution was not that strong, but I typed it on mobile, with some limitations to formatting.

• It doesn't change the core of the answer much (since blood usage is roughly estimated anyway), but a vampire must spend 1 blood point per night (if he has any) - you can't choose to rest to save that point (see p268 of V20 for that edition's rule). That means your Case A doesn't apply. Commented Jan 7, 2019 at 6:39
• Thank you. I edited and revised the entire answer in order to account for the point your raised. As you anticipated, the updated conclusion is very close to the former one. Commented Jan 8, 2019 at 7:02

Rules-wise? You spend one point of blood to wake up every evening. Assuming you never spend any blood, this means you need one point of blood each night. Otherwise healthy mortals recover one point of blood every day. From this, we can deduce that a vampire not spending blood on anything but waking only needs one person in their herd to feed on. This mortal will, of course, spend their whole life massively unwell from the constant blood loss. It's probably safer to have two, so that health issues in your herd and the need to spend blood don't mess things up.

• Question assumes frequent use of additional points, plus recovery time of four months, not one day. Can you give rules citations for the latter and rework to handle the former? Commented Jun 8, 2016 at 7:46

It depends on the population

Things that are important to know:

1. Amount of blood you need per night, "Expenditure".
2. Amount of blood taken from one victim per year (frequent donations aren't healthy, and, for long-term survival, you want to avoid frequent herd deaths), "Gain"
3. Percentage of healthy people in your population that meet the given criteria "Donors".

The formula is: Expenditure*365.25/(Gain*Donors)

For example, you spend 1 blood points per night, just staying awake, make your herd follow medical recommendations provided in Russia to only donate no more than 6 times per year (~1 blood point per time). You need 365.25 Blood Points per average year, which can be accomplished with 60.875 donors.

What goes to the amount of potential donors per population, we don't know it exactly, but we have a more interesting statistic: "Blood donation rate in high-income countries is 33.1 donations per 1000 people" according to this article. The problem is mostly not with health, but rather than with lack of well propaganda. As you don't really ask potential donors if they want to donate in your particular case, let's round it to 36 donations per year per 1000 people. This means at least 6 donors per 1000 people. In this case, you need ~10 145 people to live around you per blood point per night.

If you go for the amount of actual donors, it is widely said in russian media that 40 donors are needed per 1000 people so there is no problem with blood availability at all (for mortals), and that is possible. It doesn't mean they all need to donate 6 times per year, but again, a Tzimisce is not going to ask them. So in this case of an ideal country you have 240 donations per 1000 people per year and would need ~254 people worth of population per blood point per night.

If spending more than one blood point per night on average, multiply the numbers by the amount of blood used per night.

It is possible to make humans donate more often or give more blood per donation, but sooner or later it will kill them and damage your herd. As a Tzimisce, that's not a thing you would like. Tzimisce like order. However, if they donate X times more often or give X times more blood per donation, cut the amount of needed population by X.

P.S. Keep in mind that I don't use statistics provided in the rulebooks: they overesteem an average human harshly.

P.P.S. Remember that the main problem is the possible Masquerade breach. If such a low population is around, it is like 100% that they will be aware of what is living nearby.

Human blood is replenished in 3 months. This is why we must wait 3 months before a next blood donation.

It would be around 1 BP / week on the rules of the VTM. But, as @Tritium21 mentioned, the actual VTM rules say 1 BP / day of replenishment.

A vampire needs 1 BP / night to survive, so a single human would it be enough for him for the pure survival. If it needs 2 BP/night, then 2 humans.

If we are thinking on really long term and somehow there is the wish for a self-replenishing herd, then:

1. First, you need to know: at least 50-100 human would be needed for a completely self-replenishing population, fewer will die out because of the inbreeding.
2. The IRL blood donation rules allows people between 18 and 60 years to donate blood. Considering their mean life aorund 75 years, but considering also some problematic situations (sickness, pregnancies, etc), we could calculate that a vessel is useable roughly 50% of its lifetime.

Thus, the minimal self-replenishing herd size is 50, which means an average of 25 usable vessel. This can sustain around 12 vampires on an average 2BP/night rate.

It would be highly useful to blood bound them.

• Since you both have your own answer, rather than arguing in the comments on each other's posts, please focus on improving the case made by your respective answers on the points on which you differ. Commented Nov 22, 2015 at 22:55