Types of Vaccines
There are several types of vaccines that are designed to trigger the body to produces an immune response. Vaccines are made differently depending on the characteristics of the disease infecting agent, whether it is a bacteria, virus or toxin. There are two main types of vaccines 1) Live, attenuated vaccines and 2) inactivated vaccines.
Live attenuated vaccines
Live attenuated vacines are made up of living virus or bacteria that have been modified through a process to weaken (attenuate) and reduce it's virulence (disease inducing ability). These wild viruses or bacteria are attenuated in a laboratory, usually by repeated culturing. For example, the measles vaccine used today was isolated from a child with measles disease in 1954. Almost 10 years of serial passage on tissue culture media was required to transform the wild virus into vaccine virus . A live attenuated vaccine creates a good immune response (cellular and antibody) and often provides lifelong immunity with only one or two doses. Certain vaccines against viral diseases are made this way, eg measles, mumps, and chickenpox. Because these vaccines are live, they are contraindicated for people with impaired immunity; for example people suffering from leukaemia or HIV infection.
Inactivated vaccines do not contain live virus or bacteria. The diseases microbes have been killed by chemicals, heat or radiation. They cannot replicate and cause disease. Inactivated vaccines stimulate a weaker immune response than live vaccines and always require several doses to provide a pretective immmune response. Immunity can also diminish over time and a booster shot is required to maintain immunity. Inactivated vaccines can be composed of either whole viruses or bacteria, or fractions of either
These vaccines don't use the entire microbe, but instead are made from only part of the microbe. Scientist use the 'part' that best stimulates the immune system. Because these vaccines only use a part and not all the other molecules that make up the microbe, the chances of adverse reactions to the vaccine are lower.
These vaccines are very important especially in young infants. Some bacteria that can cause disease have a special outer coating (sugar molecules called polysaccharides) that hides them from the immune system (especially immature immune system of infants).Conjugate vaccines link these coatings to an antigen or toxiod that an immature immune system can recognize, so it can respond and produce immunity. The linkage helps the immature immune system react to polysaccharide coatings and defend against the disease-causing bacterium.
Examples of conjugate vaccines are Haemophilus influenzae type B (Hib)vaccine, pneumococcal vaccine and meningococcal vaccines in which a non toxic tetanus toxiod or non toxic diptheria protein is used as the link to stimute the immune system.
When the cause of an illness is the bacteria releasing a toxin (harmful chemical) that affects the body, a toxiod vaccine can provide protection. Scientists formulate a vaccine from just the deactivated toxin (called toxiod), rather than the whole bacteria. A toxin can be inactivated by treating them with formalin, a solution of formaldehyde and sterilized water. Toxiods are safe for use in vaccines and the immune system produces antibodies that lock onto and block the toxin. Vaccines against diphtheria and tetanus are examples of toxoid vaccines.
Recombinant vector vaccines
Vaccine antigens may also be produced by genetic engineering technology. Hepatitis B and Human Papillomavirus (HPV) vaccine ( vacine to proterct against cervical cancer) is developed this way.