Question About Vaccines and Viruses

I have two questions I have been wondering about over the past year or so:

  1. Since viruses mutate, why hasn’t the polio virus mutated so that the polio vaccine is no longer effective against it?

  2. How is it possible we have a vaccine for the COVID virus but not the common cold? I thought COVID was in the same family of viruses that cause the cold. So, why can’t we extend these vaccines to fight the common cold? Is it that their genetic profiles and mutation rates are very different?

Feel free to provide links to any scientific sources that go into more detail. I like to read articles on these topics.

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I’ll take a stab at this.

It DOES mutate and new/modified vaccines are already in use.

It also helps that the effort to eradicate polio is so extensive that the virus doesn’t get as much opportunity to mutate as more common viruses do.

The common cold is a mild illness, and vaccines are very expensive to develop and distribute. My educated guess is that it’s simply not cost effective to create a vaccine.

There is a statistic called Number Needed to Treat (NNT) often mentioned in epidemiology and drug development. It describes the number of patients that would need to be treated, in a given unit of time, to achieve a give unit of benefit. For example, a heart medication with an NNT of 50 means that 50 patients treated for one year is expected to prevent 1 fatal heart attack, or to add one year of life expectancy (one 50th of a year per person treated). From this you can work out the total cost of treatment needed to achieve the benefit, and that information is used to help decide which treatment are most cost effective.

For a long time Dialysis was a benchmark for the most expensive treatment that was still considered cost effective. It looks like dialysis costs have decreased considerably since I last looked, so the benchmark has likely changed.


You are both conflating mutation with evolution. Please stop.

That would be more correctly and clearly expressed as, "All viral replication produces genetic variation; the less replication, the less variation is available on which selection and drift can act.

If we correct @LyghtWayve’s question to, “Since viruses mutate and evolve, why hasn’t the polio virus EVOLVED so that the polio vaccine is no longer effective against it?”

I think that the answer becomes more clear.

No, that’s not accurate. SARS-CoV-2 (COVID is the disease, not the virus) is in the same family as only 3 of the viruses that cause common colds, but colds also are caused by >200 other viruses from other groups. That should answer your question.

Causing the common cold is basically an optimum evolutionary outcome for a virus. It changes the behavior of the host to increase its transmission (sneezing, coughing) while rarely killing its host. It seems likely that SARS-CoV-2 will evolve in that direction, but how long that would take is the big question.

Exactly. Unlike the vaccines we are getting for SARS-CoV-2, such vaccines may cause more deaths than they prevent.

I’m not sure. Dialysis is the only aspect of US medicine that is completely socialized. Some have described it as a racket.

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Technically, viruses don’t mutate but genomes do. These genomic changes can alter one or more properties of viruses.

Anyway you asked an important question and based on available data it seems polio virus evolution at its molecular parts targeted by polio vaccines is tightly constrained, that is, mutations at the viral components which are vaccine targets are less tolerated and this sharply reduces the risk of developing vaccine-resistant variants. Here is one nice article to read:

We don’t have a cure for the common cold for the same reason we don’t have a cure for cancer. Over 200 viruses cause the common cold, so if you get infected by one type and develop immunity against, that immunity would be useless against a different cold-causing viruses. In addition, any developed immunity to cold-causing viruses typically wane after a few months. Similarly, there is no cure for cancer because there are hundreds of different types of them: what works for one might not work for the other and what might work for one might become ineffective later on.

“COVID” is not a virus. It is a disease caused by SARS-CoV-2, a betacoronavirus. There are 4/5 human coronaviruses which cause a common cold, but one or two is a betacoronavirus like SARS-CoV-2. However SARS-CoV-2 does not cause a common cold.

As I said earlier, there are lots of cold-causing viruses to deal with. This is not the main reason though.

The most important reason is that the common cold is self-limiting and so, goes away on its own. Why would anyone spend millions trying to design, develop, test and mass produce vaccines for a disease that only gives you several days of discomfort?

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I stand corrected! :slight_smile:

The context here was a group of cardiologists discussion the pros and cons of Warfarin in combination with other drugs (I think, it’s been a long time). Warfarin is still in use so the consensus seems to be that it is worth the cost - or maybe the pharmacy racket has won another round? :man_shrugging:

Thank you. Your answer is very insightful.

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Thanks for your answer.

Note, however, I wasn’t purposely conflating mutation with evolution. I was just expressing the question at my level of understanding.


You’re welcome.

I didn’t say anything about your purpose; I asked you to stop. That conflation is a major barrier to understanding the evolution of anything.

And the misunderstanding that you were expressing goes hand-in-hand with another misunderstanding: that selection does not act on existing genetic variation, just on new mutations.

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