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Polio vaccinations
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Want to join the conversation?
- Since the Salk vaccine only gives humoral immunity, how is that is has a higher efficacy after 3 doses than the Sabin vaccine, which gives humoral and cell-mediated immunity?(6 votes)
- I tried to track down this question, the best answer I could find is that this is not yet understood. Here is an excerpt from New Generation of Inactivated Poliovirus Vaccines for Universal Immunization After Eradication of Poliomyelitis by Chumakov and Ehrenfeld (2008):
"In northern India, exhaustive efforts to increase and maintain high vaccine coverage have been thwarted by extremely low OPV efficacy. The reasons for the low efficacy are not understood; ...."
Reference
Chumakov K, Ehrenfeld E. New generation of inactivated poliovirus vaccines for
universal immunization after eradication of poliomyelitis. Clin Infect Dis. 2008 Dec 15;47(12):1587-92. doi: 10.1086/593310. Review.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2596976/
Another useful article is:
Ehrenfeld E, Modlin J, Chumakov K. Future of polio vaccines. Expert Rev Vaccines. 2009 Jul;8(7):899-905. doi: 10.1586/erv.09.49. Review.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2786268/(1 vote)
- how does the immunity pass from person to person in oral vaccine, Sabin,? is it like from a mother to her fetus or how ?(1 vote)
- The oral vaccine is given to children less than 1 yr in India. The 0 polio dose is also advocated immediately after birth. All 3 dose schedules are given 10,14 and 18 weeks since many years as per national schedule. I think you may modify the contraindication of below 1 yr.(1 vote)
Video transcript
- [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.