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The Vaccines

Watch as Olakunle Alonge reviews the history of polio vaccines and vaccination campaigns. (Step 1.10)
OLAKUNLE ALONGE: Let’s spend some time now and talk about the vaccine. Again, you cannot have an eradication goal without having an effective or efficacious intervention, in this case, a vaccine. So let’s talk about the vaccine and polio. So earlier, like we discussed, polio was an epidemic disease. So it was occurring in the US at specific months, usually the summer months when children, I mean, are more exposed to the environment. And then you have the scenario where it will come up at specific seasons. And you will have children come down with the disease and some coming down with paralysis. And there was a lot of attention to this because it was really scary, and people really didn’t understand the disease.
And there was not an interest in developing a measure, a vaccine to address this disease. So there are two major types of vaccine that were developed, the Salk vaccine, which was developed in the late 1940s, slash early 1950s, which is really using a killed version of the virus. That is to say, a version that cannot cause any infection to [INAUDIBLE] development of antibodies within the host to prevent infection with [INAUDIBLE] polio virus. So that was really the first vaccine for polio that was developed by Jonas Salk. And this is delivered using an injection, a needle. And then much later on in 1963, an oral version of the vaccine was developed.
Unlike the Salk vaccine, the oral version of the vaccine really contained the live virus, one attenuated. That is to say, that some part of the virus has been knocked off in the way that it suits– it’s no longer virulent. So some particular basis within the virus has been changed so that it doesn’t cause any virulent infection when it is administered. But at the same time, it still retains the ability to [INAUDIBLE] production of immune properties and antibodies to fight infection. So that was the oral polio virus. So we have these two vaccines– one, the injectable vaccine, which is based on the killed virus, and then the oral polio virus, which is a live virus, but it’s attenuated.
It will start to have very reduced ability to harm the recipient of the vaccine. In the picture, you see, and still talking about the Sabin virus, you will see the famous Red Sox team, really illustrating the usefulness of the oral polio vaccine or polio prevention. So this is really helpful for communication and for educating a population about the safety of the vaccine, the need for individuals to receive the vaccine, and so on. And then in the second picture, you see people lining up to receive vaccination. I mean, such a lot of the interest and the desire within the population to receive this vaccine.
So again, it really described how it was important in the early ’60s to address polio and people recognized that the vaccine, particularly the oral polio vaccine. So this was readily available, it doesn’t require an injection, was a major vehicle for achieving mass immunization and reducing the epidemic of polio virus in the United States. Now, a disease is epidemic proportional. That is to say, that it occurs at a particular period and [INAUDIBLE]. The incident rate is noticeable over that period. It’s easier to communicate effectiveness with a population of the need to use vaccines. So everybody can see the disease spreading rapidly over a period of time.
You see an increased number of cases, rapid increase in the number of cases over a period of time. So these are all characteristics of an epidemic disease, which was the way the poliomyelitis was viewed back in the early ’60s and in the ’50s, when there was a lot of interest in using the vaccine. That outlook or that perspective is different from the endemic perspective, in a scenario where the disease is almost naturally occurring in the population, and you really don’t– the characteristics is continually transmitting within the population. It doesn’t have like a specific season or a specific time when the disease transmits. So this has implication.
So communicating about the need for vaccine for an epidemic disease is different of the way that you communicate the need for vaccines for an endemic disease. So we know that the epidemic nature of the polio in the United States in the ’50s meant that it was a source of fear and dread for mothers. So it was easier to communicate the use of the vaccine, either the injectable vaccine or the oral polio vaccine within that scenario. But in most places where the Global Polio Eradication Initiative was working, mostly in low-income setting, the disease is endemic. That is to say, that it’s occurring throughout the year. There is no pattern.
I mean, there’s no epidemic pattern in which it’s classed as around a particular period. And these are simplification because the way to communicate the need for the vaccine is really peculiar, such that because there’s a lot of need to do it on a continuous basis. There’s a lot of need to repeat vaccination and so on. And therefore, there are strategies that the Global Polio Eradication had had to develop or evolve over time in order to overcome these challenges of maintaining interest in the vaccination at a global level and at the country level, and we think of a nation where the diseases are endemic over a protracted period of time.
So I would just like you to take a moment and think again about what are some of the implications for polio communications and immunization, where you are thinking about a disease that is endemic. That is to say, a disease that is year-round within a community versus a disease that is epidemic that occurs at a time-limited period, where you have your rapid increase in number of cases. What are the implications of polio presenting or manifesting as an epidemic disease in a setting and manifesting as an endemic disease in another setting?
So what are the implications for how you communicate this strategy, how you communicate the vaccine, the need for the vaccine, and how you do mass immunization within each of the settings? So just take a moment and reflect on this and discuss with small groups, if you have a small group that is listening with you, discuss.
And then, here, I would like you to also go, pause this presentation at this point, and then, go and watch the story about the polio vaccines. And let’s think about what are the different advantages, the disadvantages of the injectable vaccine, which was first discovered and the oral polio vaccine, which was later discovered, with respect to addressing academics of polio, addressing endemic transmission, and some of the challenges with the properties of the vaccines, and so on. So take a pause now and go watch the video. So what are the advantages of having the oral polio vaccine, the OPV, which we describe 11 as having a live, but attenuated, version of the vaccine. So one big advantage is that it’s really inexpensive.
It’s less than $0.20 for a dose. And it doesn’t require any trained staff to administer. And anybody can administer it. It’s just to put a drop in the mouth. And that’s it. And again, because it’s excreted into the environment– so remember when we talked about the way poliovirus replicates in the human body? It’s merely shed from the gastrointestinal tract and it’s excreted into the environment. And then, as it’s circulating in the environment, people who were not even vaccinated are exposed to this circulating virus.
And they actually and it literally seeds a generation of immune properties in those aren’t immunized in the villlage, So that they’re able to develop antibodies to the wild poliovirus, as a result of exposure to excretion of the alive attenuated virus that was excreted by individuals that were immunized. So this confers what we’ll call a “herd immunity.” So you have the benefit of the vaccination that extend beyond the people that were directly immunized. Some you have other people that were secondarily immunized as a result of exposure to the virus shedding or the vaccine shedding from the individuals that we’re immunized. So these are some of the relative advantages.
And what these advantages translate to is that it actually allows for massive, rapid deployment. So if have your normally trained health workers to give everybody the vaccine, you can readily immunize large population with the oral poliovirus. You can go door to door, house to house. You don’t need any special technique. And you can achieve a herd immunity quickly with the poliovirus. So this may be very attractive for mass-immunization campaigns, particularly in lower and middle-income country setting. And it has been the major strategy for the Global Polio Eradication Initiative in recent times. But of course, it also has some disadvantages.
So even though the vaccine is relatively inexpensive, we also know that it has a lower dose efficacy than the injectable vaccine, in many contexts. So that is to say that the ability– the effect which the vaccine is able to produce and it seeds production of immune properties in the individual, it’s lower compared to the injectable. So therefore, you need more doses on the oral polio vaccine in order to achieve immunity in the individual. And then, again, even though the vaccine, the live vaccine in the oral polio vaccine– the live virus in the oral polio vaccine has been attenuated.
That is to say, it has been changed in a way that it’s less likely to lead to an infection or virulence within the individual. We know that in rare cases, there is what we’ll call “vaccine-associated paralytic poliomyelitis,” which can occur when, over the course of application, the virus in the vaccine can regain its virulence factor. That is, it kind of regains its ability to cause harm, to cause paralysis, in an individual. And this is really significant because in the recent times, we’ve found out that these changed viruses within a vaccine can continue to circulate in the environment, right? And over the course of circulation in the environment, it can continue to gain more virulence and capable of causing paralysis.
And this has been sometimes called the “circulating vaccine-derived polioviruses.” So the oral poliovirus, in and of itself, as a [INAUDIBLE] in very rare cases can cause paralysis in some individuals, but grant it, individuals who are immunocompromised, individuals who, for some reason, who have very low immunity. And in other cases, it can change. The virus and the vaccine can change in the intestine. And it can be shed into the environment. And that circulating virus can again, cause paralysis within the human population. So again, a bigger challenge that the Global Polio Eradication Initiative faces right now, is as a result of some of these disadvantages.
So we have instances right now, where we have more cases of circulating vaccine-derived polioviruses, which are the result of use of the oral polio vaccine, are common all over the world, even much more than the wild infection due to the wild poliovirus. And then, for the injectable polio vaccine, which it contains the killed virus, the immediate advantages is that there is no risk of vaccine-associated paralytic polio. So that is that the vaccine, in and of itself, cannot cause paralysis. Right, just– we said that the OPV, the vaccine, administered to an individual can cause [INAUDIBLE] the risk of paralysis in the individual that receives the vaccine.
And that also, the risk of a modification to the virus and the vaccine in the intestine of the individual, which is shared into the environment and we can circulate in the environment. And it’ll cause the circulating vaccine-derived polioviruses, as is seen among human population. All of this does not exist with the injectable polio vaccine. And again, it produces more effective immunity in an individual. So it doesn’t require the amount of the– the per dose efficacy for the injectable polio vaccine is actually higher than the oral polio vaccine. But the disadvantage is the cost. So it’s really expensive, relative to the OPV. And there are limited capacity to really produce it rapidly on scale or like the OPV.
And then again, it also requires it to be administered by a trained health worker. So there’s that additional cost that is required, in terms of making sure that your highly-trained health worker deliver the dose. Not anybody can deliver it, unlike the OPV. So and that’s why it’s less suitable for mass immunization. But clearly, in resource-poor setting or low-income setting, the one we have with one poliovirus it’ll still be endemic. And then, it require hold of supplies, so like consumables, like sterile needles to administer it. And then again, experience, I know some parents are just very hesitant to injection. I mean, it’s a different ballgame when you put something in the mouth, as compared to when you actually inject.
And in some cases, you know that injection, in and of itself, can [INAUDIBLE] associated with increasing the risk of paralysis for people that have been previously exposed to the wild poliovirus. So again, this is all disadvantages. But to declare that you would see that both of these vaccines have their role and their relevance in an eradication initiative. So for instance, we know that the injection mode really was credited for actually helping the United States to eliminate the epidemics of poliovirus and rapidly. Much later, the oral polio vaccine came on board. But in low and middle-income country setting, the OPV has really been very helpful in rapidly scaling up a mass immunization across different context and different setting.
But now, we are seeing challenges with the circulating vaccine-derived polioviruses, which was a complication of the oral poliovirus. So again, and really a need for use of the injectable polio vaccine, which is what is under way in a lot of low and middle-income country settings. So you really do need both in order to achieve the eradication goal. Because your have three different strains of wild polioviruses– you have type 1. You have type 2, and you have type 3– the vaccine are produced in a way that they can address each of the strains. So you have the monovalent vaccine, which targets a single strain of the wild poliovirus.
You could have the monovalent oral polio vaccine type 1, or monovalent oral polio vaccine type 2, or monovalent oral polio vaccine type 3. And then, you could also have bivalent, which really can actually– vaccine that can address two strains of the wild poliovirus. And then, you have the trivalent, which combines a vaccine that can address the three different strains of the wild poliovirus. And we know that, even as we speak, that efforts are underway to produce other types of vaccines that are more stable. It’s particularly an oral polio vaccine that are more stable, with less likelihood of gaining virulence.
So that it can be used to address the scourge of the circulating vaccine-derived polioviruses, as a result of the use of the OPV, the oral polio vaccine.

Olakunle Alonge, MD, MPH, PhD Bloomberg School of Public Health, Johns Hopkins University, USA

In the lecture, you are directed to watch the video:

This is an additional video, hosted on YouTube.

As you watch, consider:

The lecturer contrasts the epidemic nature of polio in 1950s USA versus the endemic nature of the disease in places where the Global Polio Eradication Initiative is still working. What are the implications of these distinctions between epidemic and endemic disease for polio communications and immunization?

Post your response in the discussion forum.

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