Scientific research has led to the development of numerous types of vaccines that safely elicit immune responses that protect against infection.
The following are the common types of vaccines that currently exist:
Live attenuated vaccines
Live attenuated vaccines contain whole bacteria or viruses which have been “weakened” (attenuated) so that they create a protective immune response but do not cause disease in healthy people. Because these vaccines are so like the natural infections they help prevent, they produce a strong and long-lasting immune response. Just 1 or 2 doses of most live vaccines can give you a lifetime of protection against germs and the diseases they cause. However, live attenuated vaccines may not suitable for people with weakened immune systems. This is because the weakened viruses or bacteria could in some cases multiply too much and might cause illness in these individuals.
Live attenuated vaccines are mainly used to prevent the following diseases:
Inactivated vaccines are produced by inactivating a pathogen, usually using heat or chemicals such as formaldehyde or formalin. This destroys the pathogen's ability to replicate, but keeps it "intact" so that the immune system can still recognize it. Inactivated vaccines cannot replicate and always require repeated doses for immunity to be achieved. The first dose is the one that prepares the immune system to respond, but a protective immune response does not develop until the second or later doses.
Inactivated vaccines are mainly used to prevent the following diseases:
Toxoid vaccines prevent diseases caused by bacteria that produce toxins (poisons) in the body. By using toxoids, the body is able to form an immune response to the original toxin (maintained immunogenicity), but since the toxoid is a weakened form of the toxin, it cannot lead to any toxicity or toxin-induced disease. Toxoid vaccines do not offer lifelong immunity and need to be topped up over time.
Toxoid vaccines are mainly used to prevent the following diseases:
Instead of the entire pathogen, subunit vaccines include only certain components that originate from disease-causing bacteria, parasites, or viruses. These components, which are otherwise known as antigens. Although this design can make vaccines safer and easier to produce, it often requires the incorporation of adjuvants to elicit a strong protective immune response because the antigens alone are not sufficient to induce adequate long-term immunity. Subunit vaccines usually require repeat vaccinations initially and boosters in subsequent years.
Subunit vaccines are mainly used to prevent the following diseases:
(Haemophilus influenzae type b)
Nucleic acid vaccines
Nucleic acid vaccines use genetic material from a disease-causing virus or bacterium (a pathogen) to stimulate an immune response against it. Depending on the vaccine, the genetic material could be DNA or RNA. Nucleic acid vaccines work in a different way to other vaccines in that they do not supply the protein antigen to the body. Instead, they provide the genetic instructions of the antigen to cells in the body and in turn the cells produce the antigen, which trigger an immune response.
Nucleic acid vaccines are mainly used to prevent the following diseases:
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