Read this article to learn about the traditional vaccines and its drawbacks.
Vaccination is the phenomenon of preventive immunization. In the modern concept, vaccination involves the administration (injection or oral) of an antigen to elicit an antibody response that will protect the organism against future infections.
Vaccines, although in a very crude form, were used in a peculiar manner by Chinese in as early as eleventh century. They used to remove the dried scabs of smallpox patients and ground them. The so prepared powder was sprayed in the noses of healthy people. It was observed that these people were less susceptible to smallpox when there was an outbreak of epidemic.
Smallpox is a virulent disease with a high death rate. Even the survivors become victims of permanent disfigurement, blindness and mental retardation. Edward Jenner, an English Physician, observed that the farmers and milkmaids working with cows developed a mild form of smallpox called cowpox or vaccine.
And the cowpox infection could protect these people from the infection of smallpox. It was in 1796, Jenner experimentally tested this observation. He inoculated an 8-year old boy with exudate from a cowpox lesion, and he repeated it twice with a gap of some weeks. He then inoculated more human volunteers, Jenner noted that smallpox did not develop in these volunteers. This was the first discovery of the principle of vaccination.
It took nearly hundred years for the scientists to clearly understand the basis of smallpox immunity. We now know that cowpox viruses (vaccinia) inoculated by Jenner, stimulate the body’s immune system to produce antibodies which neutralize the cowpox as well as smallpox viruses. The present day vaccines which are more refined work in a similar fashion.
Vaccines are mainly of three types:
1. Dead bacteria or inactivated viruses.
2. Live non-virulent or weakened (attenuated) bacteria/or viruses.
3. Viral fragments or bacterial molecules (subunit vaccines).
A vaccine triggers the body’s immune system to produce antibodies against a specific disease— causing organism (virus, bacterium or other parasite). This provides surveillance against future exposure to such an organism and thus protects the body. Many communicable diseases (smallpox, cholera, typhoid, tuberculosis, and poliomyelitis) have been brought under control through vaccination. However, as on today, for several diseases, there are no vaccines e.g., AIDS, leprosy, filariasis.
The disease producing organisms (infectious agents) are grown in culture. They are then purified and either killed (inactivated) or made non-virulent (attenuated). This has to be carefully done without the loss of the organism’s ability to evoke immune response against a virulent form of disease-causing organism.
The traditional production of vaccines has several drawbacks:
i. It is not possible to develop vaccines for the organisms not grown in culture.
ii. The yield of vaccines is very low.
iii. Cell cultures are costly to maintain.
iv. There is a danger of non-virulent organisms getting converted to virulent ones. Vaccinations by such organisms may cause the disease itself.
v. It is not possible to prevent all the diseases by use of traditional vaccines e.g., AIDS.
Purified antigen vaccines:
Some improvements in traditional vaccines have been made by isolating the antigens from the pathogenic organisms. The antigens of bacterial cell walls (e.g., Streptococcus pneumonia causing pneumonia), and the endotoxins are good examples of purified vaccines. The endotoxins that do not possess toxicity but retain immunogenicity are referred to as toxoids e.g. toxoids of tetanus, diphtheria etc.