Vaccines are antigenic materials consisting of the whole microorganism or one of its products.

Vaccines are of 3 types:

Killed (Inactivated) vaccines: consist of microorganisms killed by heat or chemicals. They generally require to be given by a series of injections for primary immunization.

The immunity is relatively shorter-lasting; booster doses are mostly needed at intervals of months or years.

Live attenuated vaccines: consists of live bacterial or viruses which have been rendered avirulent.

They nevertheless grow and multiply in the body of the host to a limited extent.

Live vaccines usually produce long-lasting immunity. In individuals with impaired host defense, e.g.

  1. Leukemia or other malignancies, especially those receiving cytotoxic chemotherapy.
  2. Systemic lupus erythematous.
  3. Corticosteroid recipients.
  4. AIDS and other immune deficiency states.

The limited virulence of organisms in the live vaccine may be sufficient to cause a disease; live vaccines are contraindicated in them.

Two live vaccines, if not given together, should preferably be administered with a gap of 1 months.

Toxoids: are modified bacterial exotoxin so that toxicity is lost but antigenicity is retained. The term ‘vaccine’ is sometimes restricted to preparations of whole microorganisms and toxoids are enumerated separately.

Active immunization with vaccines may fail to ‘take’ during corticosteroids or immunosuppressant medication and should be avoided.

Vaccination should be differed in the presence of any acute (especially respiratory) infection and during pregnancy.

Antibiotics added during production of vaccines and present in trace amounts in viral vaccines may cause reaction in individuals sensitive to these.

Egg proteins (in vaccines prepared on chick embryo) and other materials used for vaccine culture may be responsible for allergic reactions.

Adrenaline injection (1 in 1000) should be available to control allergic reaction to the vaccine, if it occurs.

The antibodies developed in response to live or killed vaccines inactivate the bacteria/virus when it subsequently enters the body, while those induced by toxoids neutralize the elaborated exotoxin.

The latent period between vaccination and development of immunity and the period for which it lasts depends primarily on the organism, but varies somewhat in different individuals.

Viral vaccines and toxoids generally afford more prolonged protection than bacterial vaccines.

Viral Vaccines

COVID-19 vaccines: help our bodies develop immunity to the virus that causes COVID-19 without us having to get the illness.

Different types of vaccines work in different ways to offer protection. But with all types of vaccines, the body is left with a supply of “memory” T-lymphocytes as well as B-lymphocytes that will remember how to fight that virus in the future.

It typically takes a few weeks after vaccination for the body to produce T-lymphocytes and B-lymphocytes. Therefore, it is possible that a person could be infected with the virus that causes COVID-19 just before or just after vaccination and then get sick because the vaccine did not have enough time to provide protection.

Sometimes after vaccination, the process of building immunity can cause symptoms, such as fever. These symptoms are normal and are signs that the body is building immunity. Talk to a doctor about taking over-the-counter medicine, such as ibuprofen, acetaminophen, aspirin (only for people age 18 or older), or antihistamines for any pain and discomfort experienced after getting vaccinated.

Hepatitis B Vaccine: The new hepatitis B vaccine (ENGERIX-B) is prepared in yeast cells by recombinant DNA technique and contains aluminum hydroxide adsorbed hepatitis B virus surface antigen 20 micro gram in 1 ml suspension.

Hepatitis   A Vaccine: it is prepared by inactivating with formaldehyde hepatitis A virus grown in human diploid cell culture.

A single 0.5 ml, i.m. injection in deltoid muscle affords protection, but a booster dose after 6 months is recommended.

Mumps Virus Vaccine Live Attenuated: it is prepared from mumps virus grown in cell culture of chick embryo.

A single dose of 5000 TCID 50 (tissue culture infections dose 50%) affords protection for 10 years; revaccination is not required.

Measles Vaccine Live Attenuated: this is also a vaccine grown on chick embryo; available in single dose vials containing 1000 TCID 50 of Edmonston Schwarz strain (ROUVAX, RIMEVAX) or Edmonston zagreb strain(M-VAC) for s.c. injection over right deltoid region.

Rubella Vaccine: (R-VAC), it contains live attenuated rubella virus Wistar RA27/3 strain 1000 TCID 50 per 0.5 ml injection for deep s.c. or i.m. injection in upper arm.

Measles-Rubella Vaccine: two preparations of this combined live vaccine are available: have similar efficacy.

Varicella Vaccine: it is lyophilized live attenuated Oka strain of Varicella-zoster virus grown in human diploid cell culture.

Contraindicated during pregnancy, in those with lymphocytopenia and within 1 month of measles vaccination.

Mild local reaction, popular eruption and short-lasting fever occurs in 4-5% children.

Rabies: Four rabies vaccines have been produced: antirabic vaccine carbolized, Purified chick embryo cell vaccine, Human diploid cell vaccine and purified Vero cell rabies vaccine.

Poliomyelitis: The Virus (type 1,2,3) is grown in monkey kidney cell culture and two vaccines are prepared from it: oral poliovirus vaccine and inactivated poliomyelitis vaccine.

Influenza Virus Vaccine: contains inactivated influenza virus A and B. Immunization may be done annually or during an epidemic.

Influenza virus undergoes frequent antigenic changes; hence the efficacy of the vaccine is inconsistent. It is indicated only in high risk cases.

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