Vaccine: basics of the community health

Immunisation is a process of injecting vaccine in a human body. Immunisation is a key component of primary health care. Immunisation prevents 2-3 million deaths every year from diseases like diphtheria, tetanus, pertussis, influenza and measles.

What is a vaccine

A vaccine is a biological chemical or substance that increases body’s immunity and prevents the harm from disease-causing microorganisms such as viruses. Vaccines are used to prevent infection of a disease at an individual level as well as to prevent spread of these diseases to the larger population (epidemics).

How do vaccines work

A vaccine usually contains an agent that has similar structure or proteins like a particular micro-organism. So when a vaccine is injected in the body, body’s immune system treats it as that micro-organism and the protein structures called antibodies are created. These antibodies act as a memory for the next fight. So if and when the actual micro-organism enters the body, the antibodies kill it and stops it from causing harm to the body cells. This mechanism is also called as active acquired immunity to a particular infectious disease.

What are the types of vaccines

There are various types of vaccines designed to teach your immune system how to fight off certain kinds of micro-organisms — and the diseases they cause.

  • Live-attenuated vaccine

Live vaccines use a weakened (or attenuated) form of the micro-organism. The weakened virus is given to people, which can reproduce enough to generate an immune response, but not enough to make the person sick. Just 1 or 2 doses of most live vaccines can give you a lifetime of protection against a germ and the disease it causes.

Some examples of live attenuated vaccines are used to protect against: Measles, Mumps, Rubella (MMR), Rotavirus, Smallpox, Yellow fever

  • Inactivated vaccine-

Inactivated vaccines use the killed version of the organism that causes a disease. Inactivated vaccines usually don’t provide immunity (protection) that’s as strong as live vaccines. So multiple doses may be needed over time (booster shots) in order to get ongoing immunity against diseases.

Some examples of inactivated vaccines are : Hepatitis A, Influenza vaccine (Flu shot), Rabies etc.

  • Subunit, recombinant, polysaccharide, and conjugate vaccines-

Subunit, recombinant, polysaccharide, and conjugate vaccines have specific part of the micro-organism, e.g. its protein, sugar, or capsid (a casing around the germ). Hence they give a very strong immune response that’s targeted to key parts of the micro-organism. They can also be given to almost everyone who needs them, including people with weak immune systems and long-term health problems.

Some examples of these vaccines are: Hepatitis B, Human papilloma virus (HPV), Whooping cough etc.

  • Toxoid vaccines-

Toxoid vaccines use a toxin (harmful product) made by the micro-organism. That means the immune response is targeted to the toxin instead of the whole germ.

Some examples of toxoid vaccines are: Tetanus, diphtheria etc.

  • Replicating viral vector vaccine-

Scientists take a virus that doesn’t cause disease in people (called a vector virus) and add a gene that can recognise the virus spike protein. When the vaccine is given, the vector virus makes copies of itself in cells and the immune system makes antibodies against its proteins. As a result, the antibodies directed against the spike protein will prevent the virus from binding to cells and prevent infection. Example of this vaccine is Ebola.

  • Scientists all over the world are constantly working to create new types of vaccines, that are effective, easy to store and cheaper, so that they can be given to the larger population and reach to even the remotest areas. e.g. Recombinant vector vaccines (platform-based vaccines) act like a natural infection, so they’re more effective in creating a strong immune response.

What can be side effects of vaccines

Most people don’t have any serious side effects from vaccines. The most common side effect can be pain or redness at the site of injection, it is usually mild and go away quickly on their own. Some other common side effects include- Mild fever, chills, feeling tired, headache, muscle and joint pains. These common side effects can be a sign that your body is starting to build immunity (protection) against a disease. Serious side effects from vaccines are extremely rare.

Remember that getting vaccinated is much safer than getting the diseases which vaccines prevent.

How is effectiveness and safety of the vaccines ensured

  • Before a vaccine is ever recommended for use, it’s tested in labs. This process called clinical trials has a series of tests, or phases and can take several years. A vaccine is said to be effective when it protects the volunteer from the infection of that particular organism.
  • During a clinical trial, a vaccine is tested on people who volunteer to get vaccinated. Clinical trials start with 20 to 100 volunteers, but eventually include thousands of volunteers. These tests are conducted to study important areas like: safety of the vaccine, dose or amount that is most effective without any harmful effects, reaction of body’s immune system to the vaccine.
  • The drug standard authority of the country (Central Drugs Standard Control Organization- CDSCO in India) monitors the vaccine development process very closely and strictly to evaluate the vaccine’s safety and effectiveness. Any vaccine is approved only if it is proven to be effective and safe.
  • Once a vaccine is approved, the company that makes the vaccine has to test each batch of the vaccine to make sure the vaccine is Potent (It works like it’s supposed to), Pure (Certain ingredients used during production have been removed) and Sterile (It doesn’t have any outside micro-organisms). The national drug authority (For example, FDA in USA) reviews the results of these tests and also inspects the factories where the vaccine is made. This ensures that the vaccines meet standards for both quality and safety.
  • Even after the vaccine is launched in the market, or administered through the public health system, the monitoring continues for the side effects and safety.

Now let’s talk about COVID-19 vaccines.

What types of COVID-19 vaccines are being tested?

Several approaches to COVID-19 vaccine are currently being tested in several countries, including USA, England and Russia.

  • Inactivated vaccine
  • Subunit vaccine
  • Weakened, live viral vaccine
  • Replicating viral vector vaccine-
  • Non-replicating viral vector vaccine — Similar to replicating viral vector v-accines, a gene is inserted into a vector virus, but the vector virus do. not reproduce in the vaccine recipient. Although the virus can’t make all of the proteins it nee. to reproduce itself, it can make some proteins, including the COVID-3.9 spike proteim No currently licensed vaccin. use . approach.
  • DNA vaccine — The gene that codes for the COVID-19 spike protein is inserted into a small, circular piece of DNA, called a plasmid. The plasmids are then injected as the vaccine.
  • mRNA vaccine — In this approach, the vaccine contains messenger RNA, called mRNA. mRNA is procesed in cells to make proteins. Once the proteins are produced, the immune system will make a response against them to create immunity. Please note that this type of vaccines do not change the genetic makeup of a human to whom the vaccine is given.

All these vaccines are at different stages of development, and are undergoing tests for effectiveness as well as safety. Though we cannot comment on effectiveness or safety of one type of COVID vaccine over another at this stage, they will be administered ONLY if they are found to be safe at all phases of testing.

Even when a vaccine is found to be safe in population of 1 country, before it is given to the population in another country, it has to go through all phases of trials for effectiveness and safety in that country. Hence, it takes time to be launched in another country after it is found effective in 1 country.


Image sources: Pixabay

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