November 11, 2019

11: Herd Immunity in the Vaccine Era

When vaccination rates are lower, it is said to adversely affect the "herd immunity"? But, what is "herd immunity?"

11: Herd Immunity in the Vaccine Era

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Now, we talked about herd immunity in the pre-vaccine era, natural herd immunity. I want to shift now to looking at what has happened to herd immunity in the vaccine era. Just to remind ourselves, herd immunity is the presence of adequate immunity within a population against a specific infection like measles that operates to protect those at high risk of serious infection and consequently reduce morbidity and mortality from that infection.

The aim for vaccination has been to prevent infection and epidemics by the use of the mass vaccination program to protect those at high risk. And it's been done so on the promise of one dose for life, long-lasting immunity, measles elimination and eradication with the conquest of a major human disease, but these claims now have largely gone from the vaccine rhetoric and the concern now is how to maintain herd immunity in order to protect the vulnerable. For example, those who are immunodeficient for genetic reasons or whether they are on steroids or chemotherapy for cancer. These are people particularly at risk for an adverse reaction to measles virus. Because as we've seen, you need an adequate cytotoxic T cell or cellular immune response to deal with the virus. We saw that with natural herd immunity, what happens is that socio-economic circumstances act to constrain the age of measles exposure to childhood when it is least dangerous. And this is a major aspect of what we've called natural herd immunity.

The consequence of natural herd immunity is shown, for example, in this graphic that we've seen many times and I cannot emphasize how important understanding what this means. The dramatic decline in the mortality and morbidity for measles is really what natural herd immunity has achieved. That is what it has achieved. Let us look at that in a different way. With vaccination, what we have is something like this. This is what was intended, we begin to the far to my left, looking at the percentage immune on the vertical axis and age of the recipient or the population on the horizontal axis. We are born with natural immunity from our mothers, passive immunity conferred by antibodies that cross the placenta and that lasts for a variable period during the first year of life. There was no reason to suspect that vaccination would lead that to be anything other than the same as natural infection. But that declines within the first year of life, and therefore give the children the vaccine once, that has declined to a level that would allow the vaccine to work, and then we get a dramatic increase in the protective quality of the immune response to measles virus in the individual that then lasts for a very long time. Indeed, we were promised life-long immunity from a single shot.

That was what was intended. What has actually happened in the real world? Now, this is my graphic and please feel free to criticize it or reconsider it in other ways, but there are certain elements to what has happened in the real world that I want to really discuss which have a bearing on natural herd immunity versus vaccine-induced herd immunity. First of all, there is the problem that vaccinated mothers do not give their babies adequate passive immunity, so a relative deficiency in passive immunity from the mother. This was not expected, it wasn't anticipated but it is a real world consequence of vaccination. So, babies are now vulnerable in the early months of life.

Then they're given the vaccine, but the vaccine is not as protective as we thought, and it produces what is called a primary vaccine failure. A certain percentage of children who were vaccinated against measles do not develop immunity. We have this gap now between what the natural infection would produce and what the vaccine produces, primary vaccine failure. And what we have learned with time is that vaccine-induced immunity is not life-long, it's not what was promised, it actually declines and it may decline in some people quite rapidly, to points where it is no longer protective, can no longer neutralize measles virus. This is secondary vaccine failure. You can see, there is a wide disparity between what was intended, what was believed was going to happen, and what has actually happened with this vaccine.

And so, when we look at this graphic again, what has happened with vaccination in terms of the change in herd immunity that it's produced, it has taken away this constraint to maximize the number of cases of measles during childhood when it's safest and spread that age of susceptibility outwards again. At one end, in infants, by taking away passive immunity from the parents. And at the other end, by the fact that the vaccine is not 100% efficacious and people do become susceptible to measles again as adults. And so it is shifting the age of susceptibility out again to those regions where it is a more dangerous disease. Infants are now more susceptible to measles than they were before. Lack of long-lasting immunity from measles vaccine creates a pool of adults who are susceptible to more severe disease, to more severe measles later in life, and boosting of immunity using repeated doses of measles vaccine is not sustained. And we know that from the literature, the only answer to this diminishing return that is offered by the regulators and the vaccine manufacturers is to give more and more and more doses of the vaccine. Dr. Offit, one of the ambassadors for vaccination suggests now that all students should get a third dose of the MMR vaccine before entering college.

It will become apparent that this band-aid, this way of dealing with the issue by repeated doses is going to be a life-long problem because waning immunity is a long-term problem. Dr. Lyons-Weiler has written on this and calculates that in order to achieve 85% immunity in a population, the best case scenario is that you would require 14 doses of MMR. Again, this extraordinary irony that the commercial potential for this vaccine is enormous simply because it doesn't work as well as we're promised.

There was an outbreak in Quebec in 2011, and this is an interesting illustration of this problem. It was measles epidemic in the community where there was 95 to 97% compliance with measles vaccination, that's really quite alarming. Rates are of one and two-dose vaccinees, vaccine coverage among children of three years of age were 95 to 97% respectively. Among those cases there were 21 measles importations and 725 cases that occurred as a result. The overall incidents, a number of cases of measles occurring per 100,000 of the population was around nine. Again, what was alarming is the highest incidents was in adolescence. In other words, the vaccine strategy and the reintroduction of measles has led to susceptibility now in adolescence.

So people are getting the disease when it may be more serious rather than childhood when it is less serious. So, compared with an incidence of nine overall, in the teenagers, it was 75.6.

Among affected adolescents, 50% had received two doses. In other words, even with two doses, the vaccine was not working. Their conclusions were that a better understanding of susceptibility in two-dose recipients is needed, that's most certainly true. And so, if we go back to this graphic again, what we see here is this band-aid approach of giving boosters in the face of secondary vaccine failure, waning immunity. And who knows what the consequence of that is. I put these in, merely by way of illustration, but they are a question mark, because we do not know to what extent antibody immunity is boosted in terms of true protection and indeed how long that lasts, or how many vaccines any one individual is going to require over a lifetime to protect them from getting measles during a very dangerous period.

The effect on vaccination, natural immunity to mumps is another story worth bearing in mind. And we've discussed this in the last lecture, but mumps is acknowledged to be a trivial disease in children. Many don't even know that they've had mumps because the symptoms are so mild.

As I said before, it's not a trivial disease in post-pubertal males where it can cause testicular inflammation, orchitis and sterility. Mumps vaccine doesn't work and protection is way below the 96% claim by Merck on their product insert. And now mumps epidemics are occurring worldwide in highly vaccinated populations.

Mumps vaccine failure is associated with inadequate immunity following vaccination, that is primary failure, not enough people develop immunity after the injection and rapidly waning immunity after vaccination, that's secondary failure. And a third component that is rarely discussed, and that is changes in the vaccine virus over time. The vaccine virus is a live virus, it's a virus capable of mutation, indeed, it mutates quite a lot.

That is called tertiary failure. And what we started with as a vaccine all those years ago, may be very different from what we're dealing with now. These factors mean that populations are at greater risk as they grow older.

But since side effects are more common in mature males mumps vaccine has made mumps a more dangerous disease. Natural herd immunity, that is life-long immunity following exposure of children to mumps in the pre-vaccine era, has effectively been destroyed by the process of mumps vaccination.

Chickenpox is another interesting example. The chickenpox virus, varicella zoster, causes a mild self-limiting disease in healthy children. Indeed, protection of children was not the reason for the vaccine introduction, it was in fact, initially thought to keep mothers in the workplace, there was an economic reason. They didn't have to stay at home with their children with chickenpox. Perhaps not the best advertising. The virus frequency in the natural infection establishes latent infection in the cell bodies of sensory nerves, spinal nerves where it has the potential to episodically reactivate and cause shingles which is a very painful and debilitating condition.

Shingles, for example in the ophthalmic division of the cranial nerve can cause blindness. Shingles, historically, was a disease of elderly people who were immuno-depressed, they were on steroids or had other debilitating conditions that meant that their immune systems were not able to keep that virus under control.

Historically, shingles was an uncommon disease, as I say, occurring in people with immune deficiency due to cancer therapy or other immunosuppressive drug therapy. Reactivation of the chickenpox virus is inhibited in the population by an adequate level of immunity to this virus which in turn is maintained by boosting of immunity in parents and grandparents by re-exposure via their children or their grandchildren. With every epidemic of chickenpox, parents and grandparents were re-exposed to the virus, it boosted their immunity, and it kept that latent infection in nerve root under control. That way, it protected them from developing shingles.

Now, natural epidemics of chickenpox maintained herd immunity what's called by wild-type boosting of adults in this prevented shingles, that's no longer the case. The widespread use of chickenpox vaccination has removed natural herd immunity by preventing epidemics, eliminating wild-type boosting, and thereby allowing immunity to fall in individuals to a point were shingles is now much more common occurring in younger and apparently healthy people.

The reaction of the companies has, "we have caused a new disease, let's make a new vaccine." And so the commercial upside to it is we now have a herpes zoster or shingles vaccine for other older people, by virtue of creating this new epidemic of a disease with a vaccine. Somewhat ironic again.

Pertussis is another example. Within one year of the final acellular pertussis booster, and the effectiveness is reduced to around 73%, falling to 34% within two to four years. With the Tdap, which is a similar vaccine for those of six years of age and older, the efficacy drops to 69% at one year, and after four years, its effectiveness is measured at around 9%. Natural immunity may last for four to 20 years. So, we have a problem. The pattern of natural herd immunity associated with measles and the accompanying decrease in serious morbidity and mortality has been interrupted and indeed corrupted by vaccination. And this makes it very difficult to predict how vaccinated populations might respond to, say, a new strain of measles virus that has escaped the quasi protection conferred by measles vaccine.

If we put genetic selection pressure on the measles virus by an inadequate cellular immune response, and we create new mutants that are able to evade the immunity that is induced by the vaccine strain, then we have a potential problem because we create a population at risk. Vaccinated and unvaccinated who are no longer immune to this escape mutant. And if that occurs, then we risk high morbidity and mortality from measles once again.

So the exercise here is to consider, what have we learned from real world experience with these live viral vaccines? What is the broader effect of the vaccine, not just in the individual, but the effect upon the population? Live viral vaccines induce perfect... Imperfect immunity, and does imperfect immunity put selection pressure on the virus just as using antibiotics which are only partially effective against a bacterium, but encourages the evolution of bacterial resistance to antibiotics?

And please challenge the assumptions made in my graphic and come up with your own.


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