Environmental Engineering Reference
In-Depth Information
function by exposing the immune system to just enough of a pathogen to induce
antibody formation. The important part of a vaccine is the signature proteins,
which are normally expressed on the surface of bacteria or virus; these surface
proteins are unique to each infectious agent and are duly recognized by immune
system. Antibodies are formed that recognize these proteins, without the infection
actually taking hold in the body. When the individual is subsequently exposed
to the infectious agent, the antibodies neutralize the pathogen before it can enter
cells and replicate. Pathogens coated with antibodies are recognized by immune
system cells that destroy the virus or bacteria.
During the twentieth century, the burdens of many infectious diseases were
drastically reduced due to widespread vaccination campaigns. Smallpox, the only
infectious disease to have been actively eradicated by human beings, was van-
quished due to diligent vaccination efforts by the World Health Organization.
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Polio was also greatly reduced in a similar manner. Childhood vaccinations have
made rare the incidence of measles, mumps, rubella, chickenpox, and other
infectious diseases in all developed countries and many developing countries.
Recently, a vaccine for human papilloma virus (HPV), the leading cause of
cervical cancer, has been recommended for adolescent girls, with the hope of
reducing mortality from this neoplasm.
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Adult vaccines for hepatitis B, tetanus,
and rabies are also routinely used. Some vaccines need to be administered repeat-
edly, such as tetanus, due to a decline in circulating antibodies with age. Other
vaccines, such as for seasonal influenza must be administered every year since
the genetic composition and signature proteins expressed on the surface of the
virus changes from year to year.
Although vaccines have a storied and important place in the prevention of
infectious disease, they are difficult to develop since they mimic a complex
biological interaction. They have also traditionally taken decades to develop,
although new advances in molecular biology are intended to reduce development
time. Vaccines involve creating a less pathogenic (or “attenuated”) form of the
infectious agent, often by deleting genes and structures essential for replication.
While the molecular mechanisms for creating vaccine strains are well developed,
when these attenuated vaccines are used in humans, they may still be capable of
producing some disease. Therefore, the same ethical problems as were discussed
for mass administration of antibiotics and antivirals also apply to vaccination,
namely balancing the benefit to the individual with the benefit to the population.
Mass vaccination after release of a bioterrorism agent has been the focus of many
studies in recent years, and remains a viable option.
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As previously mentioned, infectious diseases need to sustain a level of inci-
dence over time in order to remain established (endemic) in a population. Vac-
cines do not prevent every case of disease in a population; they reduce the number
of new infections so that the infectious agent cannot establish itself and replicate
continuously in the population. When an infected (and infectious) individual is
placed in a population with high vaccination rates, the chances that he or she
will be able to pass along the infection is low. Not every person needs to be
