The first vaccine, for smallpox, was introduced in 1796. The World Health Organization reports that over a fifteen-year period, the measles vaccine alone prevented 17.1 million deaths. They also stated that 2-3 million deaths are prevented by vaccines in general each year. Every study I've been able to find has been focused on the last few decades.

In a world where vaccines had never been invented, how many more people would have died of vaccine-preventable disease?


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    $\begingroup$ Interesting question. I wonder if there are cases where the individual vaccine numbers would be double-counting because someone who would have died from X without vaccines would also have died from Y a few years later without vaccines. $\endgroup$ – Cort Ammon May 2 '17 at 18:13
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    $\begingroup$ Welcome to Worldbuilding, I hope you will enjoy your stay. You ask an interesting question, but it is quite difficult to answer and there is a risk that it will be closed as too broad (all "what would happen" questions are, after all, without a verifiable answer and cannot be answered better than a qualified guess). If it gets closed, then try to narrow it down and then apply for it to be re-opened. $\endgroup$ – Mrkvička May 2 '17 at 18:20
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    $\begingroup$ @CortAmmon That's an interesting thought. A report from the CDC found that in children born from 1994-2013, vaccines prevented 322 million cases of illness. There were about 76 million children born over that time period, so they assume each child would contract just over four vaccine-preventable illnesses over their lifetime. $\endgroup$ – Zenon May 2 '17 at 18:24
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    $\begingroup$ It might not be required to do so, I was just pointing out the potential chain of events (as many "what would happen" questions do get closed as too broad). Your question is not unanswerable, it is possible to model how diseases would spread if no vaccines were available and, thus, estimate how many could have died without vaccines, but we would never know if the estimate is correct or not. I, unfortunately, cannot do such estimation, but if you are lucky then maybe someone else have a good answer. $\endgroup$ – Mrkvička May 2 '17 at 18:28
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    $\begingroup$ This question is quite specific. Basically, someone do the math comparing fatality rates to years and there you go. I suppose it wouldn't hurt to narrow it down to a couple major diseases. $\endgroup$ – James May 2 '17 at 18:51

The question as asked cannot be answered, because the number of people who avoid death because of a vaccine depends on the size of the population (and on the general material level of life and hygiene of the population), and the size of the population itself in a world without vaccines is an unknown which cannot be estimated reliably.

We can however make a reasonable estimate of how many people were killed by a specific disease in a specific territory in a specific time frame. For this exercise I chose to estimate how many people were killed by smallpox in Europe from 1750 to 1850.

To compute this sum we need (1) the ratio of deaths from smallpox over the size of the population, and (2) the actual size of the population.

In Europe, as of the end of the 18th century, an estimated 400'000 persons died annually from smallpox, and survivors accounted for one third of all cases of blindness.

(From Donald A. Henderson and Bernard Moss, "Smallpox and vaccinia", in Stanley A Plotkin, MD and Walter A Orenstein, MD, Vaccines, 3rd edition, Philadelphia, 1999.)

Henderson and Moss don't say what exactly they refer to when they say "end of 18th century Europe", but let's take the population of 152 million given by Encyclopedia.com for "Europe without Russia", whatever that means. The same source gives a population of 125 million for Europe without Russia in 1750. Assuming constant morbidity and mortality, that gives about 18.2 million people killed by smallpox alone in Europe in the last 50 years of the 18th century; during the 19th century the population of Europe grew at faster pace, reaching 208 million in 1850. With the same assumptions we get 23.1 million people killed by smallpox in Europe in the first 50 years of the 19th century.

In total we have some 40 million people killed by smallpox in Europe alone in the 100 years between 1751 and 1850. For comparison, the deadly Napoleonic wars killed about 3.1 million people (worldwide, but mostly in Europe) from 1803 to 1815.

I have no idea how to extrapolate those numbers to reach the present, because after 1850 smallpox vaccination became more and more widespread, with almost universal coverage in western Europe since about 1920 or so, and in all of Europe since about 1950 or so.

Before the introduction of universal vaccination child mortality was very high; for example, in Europe from 1800 to 1850 about 1 child in 4 died before the age of 5 (from Our World in Data), and 1 in 2 died before the age of 15. This is much too much different from the modern world; just for example, in a world were each woman needs to give birth to 4 or 5 children just to keep the population stable, women will tend to have a more limited participation in the workforce, with very large effects on the economic growth.

  • $\begingroup$ Thanks for the answer! I'll take that methodology and apply it to more diseases to try to get an estimate. $\endgroup$ – Zenon May 3 '17 at 13:20

I admit I can't answer the question directly; but an interesting corollary is that the number of extra people that would have died would likely have been replaced by extra people born.

In societies extant today, those with high infant and child mortality tend to have more children to compensate, and the same was true in early America and Europe a few hundred years ago. So vaccinations as a means of preventing death is obviously more desirable than suffering through the premature deaths of half your offspring; but once the reduced expectation of child death is proven, this also leads to having fewer offspring. So the result of vaccination is fewer deaths, but (counter intuitively) not a larger total of number of people living, due to the reduced reproduction rate.

I think even without knowing the exact number of "lives saved", this might help you in parsing out the results of a world in which vaccination was not invented: Larger families, greater death losses, but about the same number of adults.

Also, in societies with high childhood death rates, presuming food is not a problem, more resources are devoted to their children (it is more expensive to try and raise 6 kids than 2 or 3), and women are culturally pressured to be more or less constantly pregnant from about 16, because the children of 16-24 year old mothers are (statistically speaking) healthier than children of older mothers.

  • $\begingroup$ Thanks for the answer, though it's more of an extended comment than an answer. I'll try to take that into account. $\endgroup$ – Zenon May 3 '17 at 13:22

Short answer, a lot. Long answer, in the big picture many people would die and people would have a much shorter average lifespan as well. Population is exponential, so it would grow a whole lot slower, since people would die off sooner. Thus leading to fewer children and less time to raise more of them. Any number of diseases could run rampant without any mass immunity. Immunity to any specific disease could only possibly spread through offspring.

Look at what happened to the Gros Michel Banana. Killed off literally all of them to extinction. Disease is powerful if unchecked.

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    $\begingroup$ Interesting points Ryan but they are more commentary than an answer to the specific question being asked. $\endgroup$ – James May 2 '17 at 18:42
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    $\begingroup$ Counterpoint, shorter lives and more frequent deaths could slow down progress. Having a lower level of development for longer could lead to a more persistent culture of many children. Thus population would in fact be higher as more children are required to garantee an heir. $\endgroup$ – Mormacil May 2 '17 at 18:54
  • $\begingroup$ In developed countries (no malnutrition), measles have a death rate of one in a thousand cases or so. Wouldn't make much of a dent in the population curve. Many other diseases practically disappear with proper sanitation. Only four diseases, to my knowledge, are fought by a worldwide vaccination program. $\endgroup$ – Karl May 2 '17 at 22:43
  • $\begingroup$ @Karl Pareto law. 80% of victims were caused by 20% of diseases. Smallpox was king. $\endgroup$ – Rekesoft May 3 '17 at 8:05

According to google, Smallpox killed 300 million people in the 20th century. This despite the fact that the disease was wiped out in first-world countries early in the century and entirely eradicated around 1970. It's been 37 years since then, and the world population is currently about double what it was over that time period, so a simple extrapolation would indicate the smallpox vaccine has prevented something like 300 million deaths since 1970.

According to the World Health Organization:

  • Measles is one of the leading causes of death among young children even though a safe and cost-effective vaccine is available.
  • In 2015, there were 134 200 measles deaths globally – about 367 deaths every day or 15 deaths every hour.
  • Measles vaccination resulted in a 79% drop in measles deaths between 2000 and 2015 worldwide.
  • During 2000-2015, measles vaccination prevented an estimated 20.3 million deaths making measles vaccine one of the best buys in public health.

Overall, I think you're safe just estimating the number of lives saved from smallpox, as the other diseases, while terrible and serious, are small-time compared to the big one. So, in summary about 300 million.

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    $\begingroup$ 2017-1970 = 47 years $\endgroup$ – user25818 May 2 '17 at 21:16
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    $\begingroup$ some math: 300M / 70Y = 4.3M / Y, * 47 years == 189M. Also, the measles vaccine was invented in 1960 and quickly adopted world wide; see historyofvaccines.org/content/articles/measles. BTW It says measles death was 1.1M as late as 2000. For the question, this is a good site with estimates of death on many vaccinated diseases; some arithmetic and extrapolation would probably put the total near 500M. But @user3294068 estimate of 300M is close enough; too: About 5% of the world population, perhaps? $\endgroup$ – Amadeus May 3 '17 at 10:40
  • $\begingroup$ My estimate of 300 million is based partly on the fact that there's a larger population now than there was in the first 2/3 of the 20th century. More people = more deaths from disease. $\endgroup$ – user3294068 May 3 '17 at 16:45

Just to further complicate your math I read this article recently that said being infected by the measles messed with your immune system for a few years. Even if you survived the initial infection you were vulnerable to other diseases such as pneumonia and diarrhea.

Additionally, mumps is known to cause sterility in men. Rubella has mild symptoms in adults but causes terrible birth defects or miscarriages. Do the children who wouldn't ever be born count for your estimates?

  • $\begingroup$ Thanks for the comment, but it's not really an answer. If I end up finding the time for this I'll see if I can't take that into account. I'd think any infection messes with your immune system for a while. $\endgroup$ – Zenon May 12 '17 at 3:18

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