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People can be vaccinated against certain diseases. Principle of vaccination is to use live attenuated load or inactivated. My question is - why we dont have vaccination against all diseases which are caused by microbes?

Rodrigo de Azevedo
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akm
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2 Answers2

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Mainly cost/benefit analysis. Using vaccines has a cost, both in dollars and in risk. That cost may be very low (cheap safe vaccines, like measles vaccine), or may be relatively high (smallpox vaccine is relatively risky, with around a 1 in 300,000 chance of moderate to severe side effects); but there is always some cost.

Vaccines may not have any significant benefit. I live in the urban USA; it's unlikely that an Ebola vaccine would offer me any benefit (as of the current situation in 2019). Very few people in 2019 have a significant chance of being exposed to smallpox, since it's extinct in the wild; the benefit of universal smallpox vaccine would be small.

So if the risk of a vaccine is greater than the benefit, delivering the vaccine would be more harmful than good. This calculation is done as a routine, and the vaccines people receive are known to be ones that confer more benefit than risk.

In fact, with vaccines, the benefit needs to be much higher than the risk, because with vaccines the benefit is invisible (nothing happens - you don't die of measles) while the risk is something that happens. Typically, vaccine benefit/cost ratios are very high, for that reason.

Monetary cost is also a factor. It may seem harsh to think that saving a child's life with a vaccine is given a price, but at some point the finite supply of money can be used more effectively elsewhere. If it costs a billion dollars to give a particular vaccine, and it ends up saving one life, is that the best use of money? Could it be better spent on nutrition, sanitation, etc?

This applies to quite a few diseases. There are, in academic labs and in the freezers of pharmaceutical companies, vaccines against a lot of pathogens that are not being used, because the cost is too great for the benefit. That's an equation that changes all the time; it applied to the Ebola vaccines at one point, but in the face of an Ebola outbreak those vaccines -- in those areas -- are now cost-effective.

Finally, there are a handful of pathogens for which a reasonably-priced good vaccine would certainly be cost-effective (HIV, malaria, tuberculosis, for example) but for which reasonably-priced good vaccines don't exist, because vaccines are sometimes really hard to make.

iayork
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    Cost-benefit also needs to look into alternative treatment options. For example, if a bacterial infection can be treated quickly, cheaply, and with few effects by antibiotics, it needs to be extremely common for vaccination to be worthwhile. – Mark Aug 21 '19 at 01:00
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    I feel like your answer would be better if you included a disclaimer at the top in bold about how incredible small the risks of vaccines are. Currently some people may misinterpret it. – Nathan Aug 21 '19 at 09:34
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    @iayork Why it is hard to make in the cases you mentioned? Using the same principles as used in other vaccinations, why we cannot make vaccine for TB, malaria, hiv etc – akm Aug 21 '19 at 13:16
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    @AmitMaurya The problem is that a vaccine is essentially a "substance" that tricks your immune system into mounting the same response it would have to the pathogen that causes the disease. The trick is to find something similar enough to the live pathogen to represent a threat, but different enough to not cause the disease in the first place. – chepner Aug 21 '19 at 14:22
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    @AmitMaurya: There actually are vaccinations for TB. They aren't used in the US because they weren't effective enough (too many strains to have to cover.) My older sister was innoculated against TB. I'm two years younger, and by that time the TB innoculation program had stopped. I was then later exposed to TB, and have some slight damage to my lungs as a result. It is not certain that an innoculation would have helped me. What is certain is that innoculation interferes with the simple "tine test" for TB. TB can be cured with antibiotics. Detection is more important than prevention. – JRE Aug 21 '19 at 14:55
  • @Amit TB immunisation is standard practice in the UK (I had my BCG at school along with all my peers); an HIV vaccine is in the works but is non-trivial to make. – Lightness Races in Orbit Aug 21 '19 at 14:58
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    Others noted that there are vaccines for TB (old, but not extremely effective) and HIV (highly experimental, so far not very effective at all). There's also a vaccine against malaria in clinical trials. All these are good examples of my point: They are not highly effective vaccines, but the diseases are so prevalent (in certain areas) and so severe that the cost/benefit analysis might become positive even with relatively ineffective vaccines. The question of why some vaccines are hard to make at all is a separate one (which I think may be answered on this site already) – iayork Aug 21 '19 at 16:55
  • @Nathan: If the reader is too lazy to note that iayork is characterizing a 1 in 300,000 chance as "risky," then they either already believe in the anti-vax nonsense, or they were probably going to be fooled by it eventually anyway. – Kevin Aug 22 '19 at 05:34
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    @Kevin I completely understand where you're coming from. But I do strongly feel that in this case, it may be better to spell it out. Some people may not understand how minuscule 1 in 300,000 is. – Nathan Aug 22 '19 at 07:16
  • @akm In the case of viruses like HIV it's due to evolution - they evolve faster than we can make vaccines for them. We have lots of vaccines for AIDS and they do work but they don't work against the current generation of the virus. – slebetman Aug 22 '19 at 18:59
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    @slebetman that's not correct, but it's off topic here and needs more room than is in the comments. – iayork Aug 22 '19 at 19:35
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I would suspect that it's because not every disease caused by microbes can be treated by vaccines. For example vaccines are not as effective on microbes that cause skin infections because the antibodies generated by being vaccinated travel in the blood and some microbes damage the skin and nearby tissues without going into the circulatory system to be detected by the immune system through antibodies.

Furthermore, when bacteria reach the blood circulatory system they cause septic shock as the body responds with an inflammatory response to both the microbe and the toxins it produces, which can be fatal. But the amount of microbes that can cause sepsis is extremely diverse: bacteria (Gram negative and positive), fungi, viruses, and parasites; sometimes it happens in combination of microbes [1]. It seems impractical and inefficient to design vaccines against every microbe that cause disease because it seems that anything that can proliferate in the blood will cause disease. Microbes can even cause sepsis without going in the blood [1].

Reference: [1] Sepsis and Septic Shock: Current Treatment Strategies and New Approaches. Gizem Polat, Rustem Anil Ugan, [...], and Zekai Halici. Eurasian J Med. 2017

user40950
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    Another factor that can limit the effectiveness of vaccines is antigenic variability in the pathogen — influenza viruses being a classic example, but also seen in many bacteria. – tyersome Aug 20 '19 at 19:48
  • @tyersome That's a good point you can edit that in if you'd like. – user40950 Aug 20 '19 at 22:51
  • @tyersome: Yeah; as I'm sure you realize, that's the same reason that people can get the flu over and over again. Another example is the malaria protozoan (Plasmodium). – ruakh Aug 22 '19 at 04:34
  • Even more extreme than the flu is the common cold. I found some research from 2016 that achieved success in animal trials, but they had to include dozens of strains in one vaccine. And I expect that, even if this comes to humans in everyday life, it would be like the flu vaccine: a shot each year with the best guess of which strains to include that year. https://www.nature.com/articles/ncomms12838 – Toby Bartels Aug 22 '19 at 16:40