Vaccines can be synthesised in many different ways, based on which they are classified. In live attenuated vaccines, pathogens such as viruses and bacteria are weakened by genetic manipulation to halt its growth and thus do not cause harm to the host. In some modified versions of live vaccines, an organism that naturally grows poorly in humans and is related to the pathogen is used. For example the Oral Sabin Polio Vaccine and Nasal Influenza Vaccine. In inactivated or dead vaccines, the disease causing pathogen is either killed or inactivated through a thermal or chemical process. The usage of such vaccines elicits a robust immune response that mimics most responses seen during an infection. Examples of such vaccines include typhoid and influenza vaccines. Acellular or subunit vaccines do not contain whole bacteria and viruses. They contain polysaccharides and proteins, which are from the surface of the bacteria and viruses. These are recognised as foreign by our immune system as it invokes immune responses against them. The various types of acellular vaccines such as Toxoid vaccine (eg: diphtheria and pertussis), Conjugate vaccines (eg: pneumococcal conjugate vaccine) and recombinant vaccine, which includes Hepatitis B vaccine. In DNA or RNA vaccines, genetic material from the bacteria or virus is introduced into the human cells. Cell machinery is employed to produce the encoded protein by the inserted genes of the pathogen. Our immune system detects such protein as a foreign agent and produces an immune response against the whole pathogen. Read details in the link below:
The Impact of vaccinations such as Diphtheria and Pertussis
