Ramblings On Vaccination

Vaccination has been hailed as one of the most important milestones in modern medicine.  Despite packets of resistance by some sectors who raised concerns on the safety and efficacy of vaccines as I have shown in my earlier post, vaccination has succeeded in eliminating some of the diseases that have plagued humanity throughout human history.  The eradication of smallpox, which was last seen in a natural case in 1977, is considered the most spectacular success of vaccination.  The next target would be polio but some isolated human populations are still beyond reach thwarting the full eradication of the disease.  But even as some individuals are not being vaccinated, either due to their remoteness or due to their outright refusal to be vaccinated, they are still indirectly protected by vaccination through “herd immunity.”  Since the majority of the population are no longer carriers or reservoirs of the disease, even individuals who are not vaccinated are indirectly conferred protection due to the absence of or of limited contagion.

Now, many may have asked if vaccination is so effective why have science not come up with a working vaccine against modern-day diseases like HIV-AIDS, influenza or Dengue fever.  The answer to that question has bearing not only on the causative disease organism but also on the workings of the immune system.

About fifty years ago, scientists reported evidence of some curious behavior by the immune system in humans and animals:  If a host was exposed to a pathogenic virus and later encountered a variant strain of the same virus, the immune system responded to the second attack largely with the same weapons it used against the first one.

Like an army still fighting by the tactics of the last war, the host immune system mostly produced antibodies matched to the first virus instead of the second, resulting in a less effective defense and whenever that same virus with a new strain attacks the host, the body will still use these weapons as the default response.  With reference to theology, this phenomenon was labeled "original antigenic sin."

We will explore this peculiar characteristic of the immune response in greater detail in our succeeding posts.