# Would a somewhat benign "vampiric" virus be doomed to infect everyone?

In one of the books of the The Witcher series Geralt has been told by a vampire (Regis, if I recall) that it was not true that vampirism could be spread by bite. He elaborated that the whole idea was ridiculous. If I recall, the argument was something like this: if that was the case, vampirism would spread exponentially, quickly infecting everyone. Since the majority of people are not vampires this shows that vampirism cannot spread by bite.

Is this true that, realistically speaking, if vampirism could be spread by bite then everyone would quickly be doomed to become vampires? Or does, contrary to this argumentation, the traditional setting where only the minority of people are infected with vampirism and vampires are largely kept at bay make sense after all?

Let's look at real world viral diseases. Rabies would, perhaps, be most similar to vampirism. To quote Wikipedia:

The virus is usually present in the nerves and saliva of a symptomatic rabid animal. The route of infection is usually, but not always, by a bite. In many cases, the infected animal is exceptionally aggressive, may attack without provocation, and exhibits otherwise uncharacteristic behavior. This is an example of a viral pathogen modifying the behavior of its host to facilitate its transmission to other hosts.

However, the window of time when the virus can infect others is relatively short:

The symptoms eventually progress to delirium, and coma. Death usually occurs 2 to 10 days after first symptoms. Survival is almost unknown once symptoms have presented, even with intensive care.

Even its name describes what it does to its victims:

The name rabies is derived from the Latin rabies, "madness". This, in turn, may be related to the Sanskrit rabhas, "to rage". The Greeks derived the word lyssa, from lud or "violent"; this root is used in the genus name of the rabies virus, Lyssavirus.

So why did rabies not infect all animals (and humans) yet? I'm not an expert, but I'd hypothesise that it is too harmful for its own good. It kills too quickly and while it makes animals aggressive to increase the likelihood of it spreading through bites it also makes symptomatic animals nigh insane and alters their looks to pretty much broadcast the message that something is seriously wrong with them and everyone should run away as quickly as they can. To quote an anecdotal report from Quora of a man meeting a rabid dog:

The dog noticed me and started running in my direction. There was something wrong - its head was cocked to one side and its jaws were slavering, the white drool around its mouth coating its matted fur.

What if there was a virus somewhat similar to rabies, but less malignant? Wouldn't it remove the obstacles of its uncontrollable spread?

To be more precise, the virus would:

• Not kill symptomatic people quickly, carriers wouldn't die much sooner than non-infected individuals;
• Not inconvenience carriers much; alternatively, it could balance off the inconveniences (eg vulnerability to sunburn) with perks (eg night vision) - what I mean here is that carriers shouldn't have a much higher chance to die because the inconveniences make them more vulnerable to other threats; in particular, it should not make carriers insane, or at least, not the majority of time;
• Like rabies, however, force carriers to display aggression towards non-carriers and a strong desire to spread the virus by biting others.

If such a virus could infect humans, would all humans soon become infected?

Perhaps mankind would spread into two camps, those not wanting to get infected and those embracing infection, two camps at a constant war with each other... But given that people could only move from the "not infected" to the "infected" camp and not the other way around, wouldn't the "infected" camp not be destined to eventually win? Also, wouldn't most people just want to get bitten ASAP if for no other reason then for the sake of peace?

To make things simpler let's assume that such "vampires" would not have to feed on blood. If they did have to drink blood then I guess the worst case scenario would be a dystopia where non-infected people would only exist to donate blood to infected people...

I would really like to somehow salvage the traditional setting, but given the above I'm not sure if this is possible... Do non-vampires have any chance?

• Could just have the virus be blood-based, the virus making it harder for them to retain iron, leading to the vampire drinking the blood of others, and needing to share his blood with another to infect them, or have it accidentally come into contact with someone's wound in combat. Vampires are then free to use their bite without risk of transmission, unless their mouth is bleeding at the time of the bite for whatever reason. People fighting vampires would then need to be careful to not have their wounds get vampire blood in them, which would make ranged combat more viable, melee a last resort. Oct 17 '21 at 12:38
• @Commoner: If they can get iron from drinking blood they can also get it from eating spinach... Blood taken by mouth does not follow a different path than any other food. Oct 17 '21 at 13:43
• @AlexP Spinach and liver has iron, yes, though I can imagine someone becoming sick/tired of eating them day in and day out when the amount of iron they could take in with blood would allow them some freedom for other things in their meals. Drinking blood for a normal person actually leads to iron poisoning/overdose if drank in excess. Vampires with a severe iron deficiency would not be negatively affected as easily, maybe even invigorated. Oct 17 '21 at 13:49

The claim makes sense, but only with some background assumptions that people in the fictional setting presumably take for granted. Specifically, let us assume that:

1. Vampires exist.
2. Vampires must bite people to feed.
3. Vampires live long enough, and need to feed often enough, that a single vampire must bite dozens (if not more) of people during their lifetime.*

Together, these assumptions imply that each vampire must bite a large number of people, and can somehow do that without being caught and killed. How they do it doesn't really matter — if vampires exist, and can survive for a long time without being slain or starving to death, that alone implies that they must accomplish it somehow.

If vampirism was easily transmitted by biting, this would imply that it would have a very high basic reproduction number ($$R_0 \gt 10$$ or so), and would thus rapidly spread through the population. Real-life diseases with such high $$R_0$$, such as measles and mumps, tend to be known as "childhood diseases" because (at least before widespread vaccination) they were so infectious that pretty much everyone caught them at a young age (and, if they survived, developed immunity that would protect them from later reinfection as adults, although not necessarily from chronic after-effects).

Besides, if vampires cannot feed on other vampires, they'll soon have a problem in this scenario, because the supply of uninfected humans will soon run out as the infection spreads exponentially.

(If they can, and can also have human children, then you're looking at a world where pretty much all adults are vampires and pretty much all children will become vampires as soon as they're bitten by a vampire parent or sibling or playmate. Even if some people attempt to protect their children from vampirism, that's going to be really, really hard when they're literally surrounded by hungry vampires, some of whom are themselves still children and lack adult self-control.)

*) There's a small loophole here: you could have both highly infectious vampirism and long-lived vampires if most newly infected vampires died before biting even one person. Those few vampires that survived past their first feeding could still live a long time and bite many people, as long as almost all of the new vampires infected by them would die before getting a chance to spread the infection further, thus keeping the average reproduction number approximately equal to 1.

The biological and/or social mechanisms maintaining such an equilibrium could be quite interesting from a worldbuilding perspective. Perhaps whatever infectious agent causes vampirism might simply be lethal to most people, with only a small fraction of (more or less) asymptomatic carriers being the actual vampires responsible for spreading it further. Or perhaps society in this setting has, out of necessity, developed strict rules that anyone showing signs of vampirism or of a vampire bite must be immediately and ruthlessly killed before they can spread the infection.

That said, while I'm not actually very familiar with the Witcher setting, I don't think either of these scenarios is likely to be compatible with it, as they imply that almost all people bitten by a vampire simply die, whether from the bite itself or due to being killed by their fellows. That seems like the kind of setting detail one would mention, if that was the case.

• A third way to maintain equilibrium would be for the vampires themselves to intentionally bite to kill in most circumstances because they understand the consequences of rampant vampirism.
– Erik
Oct 18 '21 at 7:50
• I think it's common in many fictional settings involving vampires that if a vampire takes too much blood off a victim, then the victim will die and won't have the opportunity to become a vampire. Only if the biting vampire exercises "restrain" and allows the victim to survive, will the victim turn to a vampire. BTW, "Besides, if vampires cannot feed on other vampires, they'll soon have a problem in this scenario, because the supply of uninfected humans will soon run out as the infection spreads exponentially." is the topic of the film Daybreakers
– Stef
Oct 18 '21 at 8:16
• @Erik They don't even need to care about the long term effects. Maybe vampires are hunted very fiercely, so having a newbie vampire suddenly show up would bring a lot more attention to ones already in the area. Oct 18 '21 at 14:28
• “If vampirism was easily transmitted by biting, this would imply that it would have a very high basic reproduction number (𝑅0>10)” - tell me that your answer was written in the 2020s, without telling me that it was written in the 2020s. Nov 7 '21 at 9:11
• @AndrewGrimm: The irony is that I studied mathematical modelling of infectious diseases at university several years ago. We even discussed a paper about a mathematical model of a zombie outbreak in one of our weekly seminars. (Honestly, it wasn't a very good or interesting model in my opinion.) No vampires, though, as far as I can remember. Nov 7 '21 at 12:17

Most vampire victims don't survive to turn into vampires

Most of the time, vampires drain their victims dry, killing them rather than turning them.

There's a bunch of factors, but the biggest is that vampires try and make the most of their victims and have little interest in producing more of themselves.
Remember that vampires are generally functionally immortal.
Creating a new vampire means creating competition.

Aside from that, while many vampires slip into sociopathy as a coping mechanism for their new state as a serial-killer and predator, most have some vestigial sense of morality or compassion. They don't forget being human right away.
Most vampires therefore don't want to inflict their condition on others, and don't want to kill people either.
So when they attack, they often haven't fed in a while and will find their thirst getting the better of them, resulting in them draining the victim to death.

In general, very few vampires will leave their victim alive, either for compassionate or utilitarian reasons, or just plain thirst.

# Minimal Infectious Dosage:

In theory, one vampire-infective particle is all that would be needed to cause vampirism. But in practice, life forms have immune systems that are proficient in fighting off disease. If a tiny infection starts in someone, their body mounts an immune response that fights off the infection, often before someone even realizes they were infected. This is why people might test positive for COVID, but never develop symptoms.

Diseases differ from infection to infection. What might make one person sick might not make the next person sick (especially in the immunocompromised). But more importantly, what might cause one disease to make a person sick might not work with another disease. Shigella, for example, has a minimal infectious dose only only about 10% that of salmonella, so smaller numbers of organisms can cause people to get sick with shigella than is needed to cause illness with salmonella. If, for example, a person gets sick from eating 5000 salmonella bacteria, they would get sick from eating food with only 500 shigella bacteria.

So the level of vampire infective particles might be extremely low in saliva. It's not that a bite CAN'T cause the disease, but a bite might be like a vaccinated person being in the same room (masked) with someone who has COVID. It could happen, but it's not likely. Even if a tiny infection DID happen, they would fight it off and not become a vampire (like a breakthrough COVID case with someone testing positive but never developing symptoms).

But perhaps all vampires were immunocompromised at the time of infection, or a different infectious route (blood transfer) results in a massive infectious dose. In these cases, the likelihood of becoming a vampire is very high.

• This also implies that a potential route for creating a new vampire would be repeated feedings over a period of time. That would introduce more viral agents while also weakening the immune system via blood loss. This exact pattern can be found in the Dracula novel, actually. Lucy is visited by Dracula over the course of several nights before she succumbs to blood loss and dies, then rises as a new vamp Oct 18 '21 at 12:47
• @D.Spetz Good point. I remember several vampire movies where feeding three times was the number to transform someone, with increasingly abnormal behavior after each feeding. Oct 18 '21 at 22:50

Behavior changes could isolate populations

Vampires are often described as adversely affected by sunlight - sunlight avoidance could seriously reduce infection rates in populations that spend a lot of times outdoors. It's not just that outdoors types would be less likely to get infected, but the sunlight avoidance of the vampires would tend to identify them as such, allowing the uninfected public to take measures against them.

Once the general public learns how to identify the vampires, measures against them could be more widespread.

The central issues are how easy it is to transmit and how many bites can you pull off before someone locks you up as crazy.

Particularly if the biting impulse showed up before the human shed virus.

But, by your description, people would remember being bitten. Your vampire is guilty of assault. If the saliva did not get into the wound enough , it might not infect one person before being stopped.

Humans are good at resisting aggression from other humans.

Aggressive humans exist. Humans already can be aggressive towards one another. Someone might approach me aggressively because they want my stuff, or because a guy who looked like me took his stuff, or that guy really was me, or they want to have sex with me, or they are angry because I want to have sex with them and they don't. I could keep going. A lot of human culture and societal constructs are set up to deflect or resist human on human aggression to make life in a civil society possible.

Now there are humans who approach me aggressively because they want to bite me. Join the club, Bitey! Do I need to list the ways possible to defend against aggressive acting humans? I am tempted but we will start with my attack schnauzer and my kung fu skills and end with calling the cops.

• Did you ever meet one ? most times they are very nice people. Vampires could bite you unexpectedly, or in your sleep. Or they pretend to kiss or hug you, or tell you a secret... vampires don't need to be hostile with family and friends.. they just suddenly bite you when they feel that would be appropriate. A good bite is a sign of trust and often love. They invite you to the club.. Oct 17 '21 at 23:50
• I'm not sure we're that good at resisting humans and I think it would be worse with superfast, superstrong, superdiscreet and flying "humans". (It's weird to think humans and vampires are comparable) Oct 18 '21 at 7:38

The vampires are smart, and they practice sustainable farming. If they just bite every human and convert the whole human race into vampires, there won't be a supply of humans any more, and then the vampires will go extinct too. So they intentionally bite few enough humans to keep their numbers from spiralling out of control.

New vampires must be inducted into this practice. If they act recklessly by biting too many humans, then the other vampires step in and put a stop to it, by force if necessary.

Mild spoiler alert for the general theme of some movies/shows/books...

Every vampire mythology I've read/seen has some mechanism which counteracts this quick global spreading of vampirism; and each mythology makes sure that humans are the only source of food. Here's a selection:

• The vampire may be able to decide whether his food will "turn" or not. This seems to be the case in the True Blood series; I cannot recall how they handled it - maybe it was the amount of blood extracted or it only happened if the victim died while being sucked dry, but it was a common theme that vampires would keep human familiars around as repeated blood supply, and that turning a human into a vampire placed special responsibility on the "parent" vampire.
• As an extension, the vampire society often introduces their own rules about this with whatever reasoning; for example to avoid detection, or to make sure that they don't run out of foodstuffs. This is exacerbated by mechanisms like garlic, silver or crucifixes, which gives the humans a fighting chance as soon as they become aware of the existence of a vampire in the region.
• Most vampire mechanisms conveniently have sunlight as an antidote. Sometimes, for example in the Van Helsing series, there is some cataclysmic event which reduces sunlight in some way, and thus makes the exponential spread of vampirism possible, if maybe only for a short - but long enough - time. This again gives humans a fighting chance when they are aware of the threat, by being able to move around freely during the day, and barricading themselves effectively in the night.
• Often, the vampiric society is itself structured in separate strata; for example the "elder ones", thousand years old vampires which are exceedingly powerful, or freshly bitten ones which are very much at the bottom run of the ladder. There even may be "ferals" - vampires which much reduced intelligence, which behave mostly like animals. The older ones then control the feeding of the younglings by force and strict regulations.

Also don't forget about Zombies - these are, in the spirit of your question - often exactly as exponential as you are fearing. Zombies differ from Vampires in that there is no antidote, they have no society, and can not reason for themselves; purely driven by bloodlust. Usually, a single zombie bite, or even a little scratch of a fingernail, is enough to turn a victim into a zombie. This leads to scenarios like Walking Dead or Dawn of the Dead where the whole world is quickly run over (also a special mention to World War Z which approaches the theme quite scientificial - highly recommended reading).

Summary/TLDR: a virus-based vampirism would not spread exponentially because vampires would regulate themselves to keep a steady supply of food. Secondarily, because there would be some antidotes that would be relevant if and when humans became aware of the threat.

Sollution: Vampires can choose whether to infect their victims with vampirism.

And since they're thinking, intelligent beings, they're not going to willingly create too much competition for themselves.

In any case, it’s not our fault. We were born vampires.”

“I thought you became—”

“—vampires by being bitten? Dear me, no. Oh, we can turn people into vampires, it’s an easy technique, but what would be the point? When you eat…now what is it you eat? Oh yes, chocolate…you don’t want to turn it into another Agnes Nitt, do you? Less chocolate to go around.” He sighed.

~ Terry Pratchett, carpe jugulum

Also, there's a movie that revolves around the idea of a world where vampirism has spread to almost the whole population, the vampires need human blood to avoid going insane and non-infected humans are almost extinct.

https://en.wikipedia.org/wiki/Daybreakers