As COVID-19 rages, world awaits vaccine: Here are different types of vaccines and why they are administered in different ways
Based on the type of microorganism and the type of vaccine, the route of delivery is decided.
So far, more than 24 million people have been infected with the novel coronavirus across the globe. Due to the highly contagious nature of the virus, the doctors have been struggling with the increasing number of patients flowing in the hospitals. The only thing giving hope to people all over the world is the possibility of a vaccine. But with this hope, come many questions about how vaccines work and a need to understand why different vaccines are administered in different ways.
What are vaccines?
Whenever any foreign microorganism enters the body, our immune system deploys various types of cells to the site. The microorganism is recognised as an antigen by the body and is killed by the antibodies formed by the immune cells. The body also remembers the microorganism, so the next time you get infected by the same microorganism, the antibodies can fight it off even before it starts causing any harm.
Similarly, a vaccine is either a weak, inactivated or chemically modified (toxoid) form of the microorganism, which is intentionally inserted into the body. Once exposed to the vaccine, the body’s immune system forms antibodies against the microorganism, thus providing protection from it in the future.
What are the types of vaccines?
There are four main types of vaccines, which include:
1. Live-attenuated vaccines: These vaccines use the weak form of the infection-causing microorganisms. Since they are similar to the microorganisms in case of a natural infection, they create strong and long-lasting immunity. MMR (measles, mumps, rubella) vaccine and chickenpox vaccine are examples of live-attenuated vaccines.
2. Inactivated vaccines: These vaccines use the dead form of the infection-causing microorganisms so they require a booster dose. Flu shots given to adults are an example of the inactivated vaccine.
3. Subunit, recombinant, polysaccharide and conjugate vaccines: These vaccines use either the protein, sugar, or capsid (outer coat) part of the infection-causing microorganism. HPV vaccine and hepatitis B vaccine are some of the examples of such vaccines.
4. Toxoid vaccines: These vaccines use a toxin formed by the infection-causing microorganism. Tetanus toxoid is an example of toxoid vaccines.
How are vaccines delivered to a person?
A vaccine can be delivered in different ways, such as:
1. Intradermal (ID): Intradermal vaccines are injected into the top layers of the skin. BCG vaccine is delivered intradermally.
2. Subcutaneous (SC): Subcutaneous vaccines are injected into the fatty tissues between the layer of the skin and the muscle. MMR vaccine is given subcutaneously.
3. Intramuscular (IM): Intramuscular vaccines are injected into the muscle. Tetanus toxoid is injected intramuscularly.
4. Oral: As the name suggests, oral vaccines are given by drops into the mouth. Polio vaccine is given orally.
5. Intranasal: Vaccines can also be delivered intranasally such as type of influenza vaccine, which is delivered through a nasal spray to children.
Painless vaccinations are also delivered to children with the help of jet injectors, microneedles and nano patches.
Why vaccines are delivered through different routes?
Based on the type of microorganism and the type of vaccine, the route of delivery is decided. Vaccines that contain adjuvants (components that increase the efficacy of a vaccine) are administered intramuscularly as they tend to cause irritation, inflammation, skin discolouration, loss of elasticity of the skin, and sometimes granuloma formation if injected into subcutaneous tissue.
Most inactivated vaccines contain adjuvants so they are given intramuscularly, while most of the live attenuated vaccines are given subcutaneously. The subcutaneous route of vaccine delivery is chosen for live attenuated vaccines as it is less painful and reduces the chances of abnormal bleeding.
Some vaccines are given intramuscularly because muscles have good blood flow, thus, the vaccine gets quickly absorbed by the blood vessels.
For more information, read our article on Painless vaccine.
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