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What Are Vaccines, And Why Are They Not Given Intravenously?

coronavirus vaccine


Antibodies are proteins capable of killing any bacteria or virus that enters the human body. Production of a specific type of antibody against a particular disease takes place when a person is vaccinated.

An antigen is a substance that causes your body to produce antibodies. An antigenic element induces your body to produce antibodies.

Vaccines are biological substances that contain antigenic components. The human body produces antibodies against the antigenic component with every injection of a vaccine. The person who received the vaccine will not get sick because the antigen is a killed or weakened bacteria, virus, or microorganism. After vaccination, your body has developed antibodies against a particular disease-causing microorganism. Exposed to the active disease, you will not get sick because your body is prepared and has antibodies against it. Said antibodies keep circulating in your body, protecting you from future exposure to the same disease.

Types of vaccines

Live attenuated vaccin
  • Inactivated vaccines. These vaccines also fight viruses and bacteria. Inactivated or killed viruses or bacteria serve as the antigens in these vaccines. Polio and the Sinovac Covid-19 vaccines are examples of this type.
Inactivatd vaccines
Inactivated vaccines
  • Toxoid vaccines. The antigen placed in the vaccine is a toxoid (weakened toxin). Hence, this type of vaccine neutralizes toxin-producing bacteria. When the immune system meets a toxoid, it learns how to fight the natural poison. These are the vaccines used for diphtheria and tetanus toxins.
  • Subunit vaccines. The antigen placed in the vaccine is a part of the virus or bacteria instead of the whole germ. For this reason, side effects are minimal. It prevents pertussis or whooping cough.
  • Conjugate vaccines. They fight a particular group of bacteria with antigens covered by sugar-like substances known as polysaccharides. The coating prevents the immature immune system of children from recognizing an antigen. Hence, the conjugate vaccine connects to the polysaccharide, an antigen that the immunity system can recognize and respond to accordingly. This vaccine prevents Haemophilus influenza.
  • mRNA vaccines. These vaccines contain mRNAs that teach your cells to produce spike proteins. When your immune system recognizes the spike proteins, your body produces antibodies against them. When the active COVID-19 disease enters your body, the antibodies formed before your infection will fight them off. Hence, you will not show the clinical manifestations of COVID-19 infection. Examples of mRNA vaccines are the Pfizer-BioNTech and Moderna Covid-19 vaccines.
mRNA covid-19 vaccines
mRNA covid-19 vaccines
  • Viral vector vaccines. These vaccines contain adenoviruses, each one carrying DNA. When this adenovirus enters the host’s cell, it goes near its nucleus and injects the DNA inside. This DNA then produces the mRNA affecting the multiplication of T cells and inducing the B cells to generate the necessary antibodies. Examples of this are the Oxford-AstraZeneca, Sputnik V, and the Johnson and Johnson Covid-19 vaccines.

Routes of administration

  • Intramuscular. One of the muscles receives the vaccine injection.
  • Intradermal. A part of the skin takes in the vaccine injection.
  • Subcutaneous. An area under the skin serves as a reception for the vaccine. 
Intramuscular, subcutaneons, intravenous, intradermis

Reasons for not administering vaccine via the intravenous route

  • Vaccines have crystalline aluminum salt as one of their ingredients. The salt adsorbs the antigens that, when injected into the muscle, are gradually released over time. This gradual release of the antigen serves as a continuing stimulus for sustained antibody production. If injected intravenously, all of the antigens enter the circulatory system all at once and so fast that the antigenic effect immediately wanes, producing lesser antibodies.
  • A vaccine given intramuscularly inflicts some reactions. Intravenous injections will cause more severe reactions that the patient may even die from it.
  • The muscle, especially the deltoid or the anterolateral aspect of the thigh, is the preferred site for injections. These muscles have an abundant blood supply reducing the harmful effects of the substances injected into them. An intravenous route increases the likelihood of possible harmful effects because the vaccine is immediately inside the circulation. Thus, the reaction to the vaccine is immediate and more severe.
  • The musculature has an excellent blood supply that helps to disperse the vaccine. In addition, muscle contains and recruits immune cells called dendritic cells that take up the antigens quickly and stick them on their surface like flags. Dendritic cells then migrate to and slip into lymph nodes, where they encounter the T and B cells, also known as T and B lymphocytes. These T and B lymphocytes are blood cells that protect the human body against specific disease-causing microorganisms. Upon meeting the T and B lymphocytes, the dendritic cell presents the antigens on its surface. When the antigens are recognized, the T cell multiplies while the B cells generate the necessary antibodies. Injecting intravenously, this process could not take place.
  • The muscle serves as a ready pool of dendritic cells. These dendritic cells pick up the antigens brought by the vaccine. Thus, the musculature serves as a depot for the dendritic cells-antigen combination. With this setup, gradual exposure of the antigens to the T and B lymphocytes takes place. This extended exposure results in greater activation of the immune system. Injecting intravenously this will not happen.

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