Vaccines and Immunization: Covid-19 Vaccine Development

By Sudheer Kumar K|Updated : November 2nd, 2020

Diseases and Vaccines are important topics in UPSC IAS Mains GS Paper-III (Science and Technology). Hence this article covers different vaccine types in the context of Covid-19 vaccine development.


Table of Content


A vaccine is a biological preparation (drug or medicine) that provides active acquired immunity to a particular infectious disease like Ebola, Covid-19 etc. Vaccines train the immune system to create antibodies, just as it does when it’s exposed to a disease.

Vaccines often contain small amounts of dead or weakened forms of viruses or bacteria or parts of them.  Some vaccines contain inactivated toxins that are produced by disease-causing bacteria. However, since vaccines contain only killed or weakened viruses or bacteria, they do not cause the disease or put an individual at risk of its complications.

Vaccines are safe and effective as they are tested before they’re recommended for use. Clinical trials are conducted before roll out for public use.

The administration of vaccines is called vaccination. Vaccination is the most effective way of preventing infectious diseases.


Immunisation is a process whereby an individual is made immune or resistant to an infectious disease typically by administering the vaccination. The vaccine stimulates the individual’s immune system so that it can recognise the disease and protect the individual from future infection. So, immunisation is what happens in your body after you have the vaccination.

Government of India is providing vaccination free of cost against vaccine-preventable diseases include diphtheria, pertussis, tetanus, polio, measles, severe form of childhood tuberculosis, hepatitis B, meningitis and pneumonia (Hemophilus influenza type B infections), Japanese encephalitis (JE) in JE endemic districts and newer vaccines such as rotavirus vaccine, IPV, adult JE vaccine, pneumococcal conjugate vaccine (PCV) and measles-rubella (MR) vaccine under Mission Indradhanush.

According to the World Health Organisation, some vaccines are currently under development or being piloted, including those that protect against Ebola or Malaria but are not yet widely available globally.

And the most recent one is a vaccine for Covid-19 pandemic, a variant of SARS Cov-2 virus.

Types of Vaccines

Let see now, how vaccines are developed and different types of vaccines. There are several different types of vaccines. Each type is designed to direct the immune system how to fight off certain kinds of germs — and the serious diseases they cause.

While creating vaccines, scientists consider:

  • How your immune system responds to the germ or virus
  • Who needs to be vaccinated against the germ
  • The best technology or approach to creating the vaccine

On the basis of these factors, scientists decide which type of vaccine they will make. There are 4 main types of vaccines:

  1. Live-attenuated vaccines
  2. Inactivated vaccines
  3. Subunit, recombinant, polysaccharide, and conjugate vaccines
  4. Toxoid vaccines

1. Live-attenuated vaccines

  • Live vaccines use a weakened form of the SARS Cov-2 virus that causes a disease.
  • Since these vaccines are so similar to the natural infection that they help prevent, they create a strong and long-lasting immune response.
  • Just 1 or 2 doses of most live vaccines can give you a lifetime of protection against a germ (in our case SARS Cov-2 virus) and the disease it causes.
  • Some limitations of using Live vaccines:
    • As they contain a small amount of the weakened live virus, people with weakened immune systems, long-term health problems, or people who’ve had an organ transplant should consult their health care provider.
    • Live vaccines need to be kept cool. That means they can’t be used in countries with limited access to refrigerators.
    • This method requires extensive safety testing.
  • Live vaccines are used to protect against Measles, Mumps, Rubella (MMR combined vaccine), Rotavirus, Smallpox Chickenpox and Yellow fever.

2. Inactivated vaccines

  • Inactivated vaccines use the killed version of the germ (SARS Cov-2 virus) that causes a disease.
  • Inactivated vaccines usually don’t provide immunity (protection) that’s as strong as live vaccines.
  • Hence several doses over time (booster shots) are needed in order to get on-going immunity against diseases
  • Inactivated vaccines are used to protect against:
    • Hepatitis A
    • Flu
    • Polio
    • Rabies

3. Subunit, recombinant, polysaccharide, and conjugate vaccines

  • Subunit, recombinant, polysaccharide, and conjugate vaccines use specific pieces of the germ — like its protein, sugar, or capsid (a casing around the germ).
  • Since these vaccines use only specific pieces of the germ, they give a very strong immune response that’s targeted to key parts of the germ.
  • Some scientists using protein-based vaccines, where Coronavirus proteins are directly injected into the body.
  • According to the Nature report, fragments of proteins or protein shells that mimic the coronavirus’s outer coat can also be used for vaccine development.
  • These vaccines can also be used on almost everyone who needs them, including people with weakened immune systems and long-term health problems.
  • Limitation: Need booster shots to get on-going protection against diseases.
  • These vaccines are used to protect against:
    • Hib (Haemophilus influenzae type b) disease
    • Hepatitis B
    • HPV (Human papillomavirus)
    • Whooping cough (part of the DTaP combined vaccine)
    • Pneumococcal disease
    • Meningococcal disease
    • Shingles

4. Toxoid vaccines

  • Toxoid vaccines use a toxin (harmful product) made by the germ that causes a disease.
  • These vaccines create immunity to the parts of the germ that cause disease instead of the germ itself. That means the immune response is targeted to the toxin instead of the whole germ.
  • Need booster shots to get on-going protection against diseases.
  • Toxoid vaccines are used to protect against:
    • Diphtheria
    • Tetanus
    • The future of vaccines

Some other types of vaccines include:

Nucleic-acid vaccines

  • Scientists aim to use genetic instructions, in the form of DNA or RNA, for a coronavirus protein that prompts an immune response.
  • In this type of vaccination, the nucleic acid is inserted into human cells that churn out copies of the virus protein.
  • Most of these vaccines encode Corona virus’s spike protein
  • DNA and RNA based vaccines are safe and easy to develop.
  • To produce them, only genetic material is required and not the virus itself.
  • However, these vaccines help in stimulating both the humoral and cellular arms of the adaptive human immune system.
  • This type of vaccine at the moment is being used against the influenza virus, hepatitis B virus and rabies.

Recombinant vector vaccines (platform-based vaccines):

  • The use of attenuated (weakened) vaccines is too risky for pathogens such as HIV.
  • Hence a safer alternative is to develop a live, recombinant vector vaccine where one or a few pathogen genes with immunogenic activity (proteins that elicit protective immunity) are expressed from a benign virus vector.
  • They act like a natural infection, so they're especially good at teaching the immune system how to fight germs.

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