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- [Voiceover] So recently I got into a conversation about the world's greatest medical achievements. And we were wondering, we were trying to think, what is the world's greatest medical achievement? And, after some long thought, you know, I was putting some deep thought into it, I came to the realization that vaccinations are kind of an astounding medical achievement. In fact, maybe even the world's greatest medical achievement. And I think antibiotics come very close. And the reason it's such a great medical achievement is because with vaccines, and antibiotics as well, there is the potential to completely wipe out a disease that affects humans. Completely eradicate it. And we've come kind of close with polio. Polio is effectively eradicated from the western hemisphere of the world. And it's all thanks to vaccinations and immunizations. Unfortunately it still exists in some recesses, some corners of the world, but I think it's very cool that we've come very close. So I want to dive deeper into how these vaccinations work. And for polio, there are really two major types of the vaccination. There were two major vaccinations that were created. There's the Sabin vaccine, so the Sabin form. And there's also the other form, which is known as Salk. So the Sabin polio vaccine and the Salk polio vaccination. So what's the difference between these two? So the Sabin vaccine is actually considered, it's a live but attenuated vaccine. And attenuated just means decreased in effectivity. So the vaccine itself is actually effective. With three doses of the vaccine it has about a 95% effectivity. So it's 95% efficacious. So attenuated just really refers to the virus itself. So in this vaccine, the virus is actually alive, but it's no longer virulent. The scientists that created this vaccine removed the ability for the virus to cause damage to the cells of our body. So the virus can not cause damage to the body any more. Now the Salk vaccine, on the other hand, is a killed form of the virus. So it can't even replicate. It's just completely dead. And this is also a very efficacious vaccination. So with only one dose it's about 90% efficacious, and after three doses it's 99% efficacious. So it's a very effective vaccination. And the other major difference between these two is the Sabin vaccine is a liquid medication, so it comes in a bottle of liquid and you can drink it. Whereas the Salk vaccine is injected, so it's considered intramuscular. Injected into the muscle through a needle, through a syringe. So already you can see a lot of differences between these two, but what are the advantages or disadvantages of either of these? Well let's dive a little bit deeper. The benefit of the Sabin vaccination is it induces both humoral as well as cell-mediated immunity. Whereas the Salk vaccine really only induces humoral immunity. So there's no cell-mediated immunity with the Salk vaccination. So what does that even mean? So what does that mean? What is humoral versus cell-mediated immunity? Well first let's take a look at humoral. So let's take a look at a bunch of cells of the body. So are a bunch of cells of our body and let's say the nasty virus, the polio virus, which is this little green guy in here, gets into the body. Now it's floating around in the interstitial fluid, so it's floating around in the body, it's looking for cells to infect right now. Remember, viruses get inside cells and then replicate, so create more copies of themselves, and then they burst out, all these new copies. So in our body we have certain white blood cells and responsible for the humoral immunity are these white blood cells called B cells. And B cells are kinda cool. They're actually among my favorite cells. They create what are called antibodies, right? And these antibodies are these little Y-shaped proteins that end up finding something they recognized and attach to it. So when your body is exposed to the polio virus, some B cells of the body will recognize this virus, they'll recognize it and they'll create antibodies that will bind to it. And this alerts the B cells that there's something wrong and they call out to other reinforcements, other cells of the body, and these reinforcements come and help wipe out the virus. So the reinforcements come in and knock out all these viruses. So that's great. However, the major problem is that once the virus gets inside of a cell, the B cell can no longer do anything. So a B cell comes along, sees the cell, and thinks, "Oh, there's nothing wrong," and then continues on its merry way. So it doesn't do anything. So that's the problem with humoral immunity. Once the cell is infected, there's no way for a B cell to get to it. Now with cell-mediated immunity, so we'll draw the cells of the body again, and let's say we've already been infected, right? And for good measure, let's put another normal cell over here. So B cells can't get these guys, but there's other white blood cells of the body known as T cells. And T cells are specialized at recognizing when a cell is sick. So when another cell of the body is sick, these cells actually send a distress signal to the T cell and say, "Hey, come over here, I'm sick. "You need to help me out." Now unfortunately because they're already infected, there's nothing these T-cells can do except make sure that they eliminate the threat. So the kill off these cells. And so that's cell-mediated immunity, from cell to cell. So the Sabin vaccine creates greater immunity because it induces both humoral and cell-mediated immunity. Whereas the Salk only induces this humoral immunity over here. Now the Sabin vaccine is also very cheap, it's not too costly. Whereas creating an injectable vaccination is more costly than this oral dose. And another great thing about this Sabin vaccine is the immunity can actually be passed from person to person. So let's draw some people here. And you'll see, if we take this virus, right? This is the live, attenuated form of the virus, and we give it to this person, it still replicates. So it actually, it's an enterovirus, it replicates in the intestines, but also in the throat too. So it replicates in this person and can actually be passed on to these other people. Now the beauty of this is since this virus is not virulent, it's attenuated, it can't do any damage, it gets passed on and confers immunity to these other people. So they get the immunity. Whereas with the Salk vaccination, the virus in this vaccine are dead. So we provide immunity to this person, we'll create this little bubble around them, so they're immune, but they can't pass it on. So the immunity, it stops right there. And going back over here, these guys are immune, they received the immunity when the virus is passed on to them. So from a population health standpoint, you can reach a larger number of people using this Sabin vaccine versus the Salk vaccine. So in areas where it's very challenging and very difficult to reach people, the oral vaccination form is used. However, in places like the United States, where it's often required to get a vaccination, it's much easier to locate people and provide them with immunity. So now looking at these two, it seems like the Sabin form of the vaccination is much better than the Salk form. Oh, and before I continue, I should have shown you this a little bit earlier. You can remember the names of these vaccinations by looking at the letters. So Salk has a K, that's the killed form of the vaccine, where Sabin has an N and that's the attenuated form of the vaccination. So that can help with remembering which is which. So now going back and looking at these, it looks like the Sabin form is more advantageous, there's more advantages. However, it's not without its disadvantages. The two major disadvantages that I see with the Sabin vaccine is if there's another enterovirus, so polio's an enterovirus and some examples include the rhinovirus, echovirus, coxsackievirus, all of these are enteroviruses. If an enterovirus happens to affect this person at the same time as they're getting this oral form of the vaccine, this other virus can interfere with the immunity. So the immune system, so let's say this other enterovirus is in here replicating. The immune system doesn't know that vaccine introduced is not dangerous and so it tries to fight both of these off and can get overwhelmed. And a person may not gain immunity from the polio virus. And in parts of the world where there isn't proper health care, this can be a huge problem, because individuals might be afflicted by other viruses at the same time. So you have to really think about this. And another major issue is very rarely, and I want to put the numbers down here, one in 2.5 million people that receive the live form of the vaccination can sometimes have something where one of the live viruses may transform and become virulent. This is a very small number and a very small risk, but it's still a risk. And if this virulent strain now takes over it can infect the patient and they can contract polio. So because of this, never, never, never, never give the live vaccine to somebody who is immunocompromised. So if somehow their immune system is not functioning properly, this gives the virus more time to revert to this virulent strain. So never give the live vaccine to somebody who has an ineffective immune system. And this is the same reason you never give the oral vaccine to an infant younger than one year old. And also pregnant women. And really anybody who has a close contact to people of this demographic. So you don't want to give it to a mother who has a one-year-old child either. Or to somebody who lives with their very elderly, sick grandparent, or something like that. However, again from a population standpoint, this can be very effective at reaching a larger number of people much more quickly. So in summary, it's important to undertstand the differences between these two so that you can know the advantages and disadvantages of using either one.