The world is waiting with bated breath for a functional COVID-19 vaccine. In the past century, vaccines have rescued humankind from many infectious diseases.
What makes designing a potential vaccine for COVID-19 challenging? To answer this question, it is important to understand how a vaccine elicits an appropriate immune response in the body.
Active and passive immunisation
The immune response towards any infection can be passive or active. Passive immunisation is when antibodies are directly transferred from one individual to another. Such passively transferred antibodies accord immediate protection but it wanes gradually and the individual eventually becomes susceptible to the disease again. It could be natural or artificial.
Placental transfer of antibodies from the mother to the foetus gives natural passive immunity. Convalescent plasma therapy, involving the transfer of plasma containing specific antibodies from recovered individuals to susceptible individuals, provides passive immunity as well.
Vaccines provide active immunisation: they deliberately introduce a foreign substance, called an antigen, into the body to induce the body to mount an immune response. Though the protection is not conferred immediately, the immunity lasts for a considerably longer period once established. Repeated doses of the same antigen could boost immunity further.
How does a vaccine work?
A vaccine works like a virus and initiates an immune response but without causing major illness.
The immune response is brought on by different types of cells. However, a specialised group of white blood cells, called the B and T lymphocytes, are important to sustain the immune response in the long run.
When an antigen enters the body, cells called dendritic cells get attracted to it, and then carry the antigen to T lymphocytes. The T lymphocytes identify these antigens and bind to them.
Meanwhile, B lymphocytes also pick up the antigens, process them and present them to the T lymphocytes. After this interaction, T lymphocytes release signalling molecules called cytokines, which stimulate the B lymphocytes. In response, the B lymphocytes rapidly turn into plasma and memory B cells. One B lymphocyte can produce thousands of such daughter cells in a few days.
The plasma cells are responsible for secreting antibodies that will tackle the antigen and eliminate the infection. And once the infection has been removed from the body, the plasma cells die while memory B cells rest in the bone marrow, and keep secreting low levels of antibodies.
When the body is exposed to the same antigen again, the circulating antibodies bind to the antigen. This is what they mean when they say the immune system becomes familiar with the antigen, and the immune response the second time is even more effective. This memory is known as immunological memory, and it forms the basis of vaccination.
Live attenuated and inactivated killed vaccines
Ideally, a vaccine should trigger an adequate immune response without harming the body. There are different types of vaccines to achieve this outcome. Conventional vaccines fall into two broad categories: live attenuated vaccines and inactivated killed vaccines.
Live attenuated vaccines contain whole virus particles. Inducing the virus to replicate under unnatural conditions reduces its virulence. For example, researchers could have injected the virus into an unnatural host, causing the virus to eventually lose its adaptation towards the actual host, and transform to a less virulent form. That is, it can no longer cause disease as well as it could before. This process is called attenuation.
The level of attenuation is critical to a vaccines success. Over-attenuation could render the vaccine ineffective, while under-attenuation could cause the vaccine itself to produce disease.
The chickenpox, measles, mumps and rubella vaccines are all live vaccines.
Inactivated vaccines contain a part of the virus instead of the whole. During preparation, researchers remove those parts of the virus required for viral replication, making these vaccines safer than the live attenuated type.
On the flip side, inactivated vaccines in general dont accord long-lasting protection, like live vaccines. Sometimes, a substance called an adjuvant is added to inactivated vaccines to boost the immune response and make them last considerably longer. However, including an adjuvant increases their overall cost.
The COVAXIN vaccine against COVID-19, developed by Hyderabad-based Bharat Biotech, is an inactivated vaccine with alum as adjuvant.
DNA vaccines
Apart from conventional vaccines, in the last few years, researchers have tried a new generation of vaccines. One of them is a DNA vaccine. The ZyCoV-D vaccine being developed by Zydus Cadila is of this type.
Cells have DNA in their chromosomes and also outside the chromosomes in a form called plasmids. First, researchers obtain plasmids from a bacterium. Then, they separate some genetic material from the virus and insert it into the plasmid, and inject this plasmid into the body.
The viral genes then integrate themselves into cells in the body and begin to express foreign proteins. This triggers an immune response.
Plasmid DNA can be easily constructed and manipulated by genetic engineering. So its not hard to produce DNA vaccines in large volumes which then means they are quite cost-effective.
However, although experiments with DNA vaccines on animal models have been successful, not one is currently available for human use. One reason is that DNA vaccines have been found to elicit a less pronounced immune response in humans than in animals. Scientists are working on several strategies to overcome this shortcoming.
In this context, if ZyCoV-D successfully completes human clinical trials and is found to be efficacious (and safe), the occasion will undoubtedly break new ground in the history of vaccines.
Niranjana Rajalakshmiis a veterinary microbiologist.
Read the original post:
Explained: How Different Vaccines Work, Including COVAXIN and ZyCoV-D - The Wire
- Who are We? - November 7th, 2009 [November 7th, 2009]
- Vilsack targeted for his Pro-GMOs stand - November 7th, 2009 [November 7th, 2009]
- Call for technology to produce cellulosic ethanol - November 7th, 2009 [November 7th, 2009]
- Kenyan scientists weigh on GMOs - November 7th, 2009 [November 7th, 2009]
- Indian researcher makes a case for biotechnology - November 7th, 2009 [November 7th, 2009]
- Michigan smoothens the way for alternative energy investors - November 7th, 2009 [November 7th, 2009]
- Link of ethanol use to high food prices questioned - November 7th, 2009 [November 7th, 2009]
- EU challenges France on GM Maize - November 7th, 2009 [November 7th, 2009]
- POET rolls out cellulosic ethanol plant - November 7th, 2009 [November 7th, 2009]
- There’s a bright future for cellulosic ethanol investment - November 7th, 2009 [November 7th, 2009]
- Cellulosic ethanol can considerably reduce gasoline use by 2030 - November 7th, 2009 [November 7th, 2009]
- Human Genetic Engineering - Background - November 7th, 2009 [November 7th, 2009]
- Human Genetic Engineering - History - November 7th, 2009 [November 7th, 2009]
- Human Genetic Engineering - Methods - November 7th, 2009 [November 7th, 2009]
- Human Genetic Engineering - Uses - November 7th, 2009 [November 7th, 2009]
- Human Genetic Engineering - Controversy - November 7th, 2009 [November 7th, 2009]
- Human Genetic Engineering - In popular culture - November 7th, 2009 [November 7th, 2009]
- Human genetic engineering - An Introduction - November 7th, 2009 [November 7th, 2009]
- Human Genetic Engineering - A Very Hot Issue! - November 7th, 2009 [November 7th, 2009]
- What are the risks of genetic engineering in humans? (human genetic engineering) - November 7th, 2009 [November 7th, 2009]
- What are the benefits of human genetic engineering? (human genetic engineering) - November 7th, 2009 [November 7th, 2009]
- Genetic Engineering - Ethics and Controversy - November 7th, 2009 [November 7th, 2009]
- Genetic Engineering Ethics In Science Fiction - November 7th, 2009 [November 7th, 2009]
- Genetic Engineering Ethics - November 7th, 2009 [November 7th, 2009]
- Welcome to Pest Control Exterminator Network - December 13th, 2009 [December 13th, 2009]
- OMD - Genetic Engineering - August 27th, 2011 [August 27th, 2011]
- X-Ray Spex - Genetic Engineering - August 27th, 2011 [August 27th, 2011]
- Ancient Alien Nephilim, Giants, Mutants, Genetic Engineering, and Hybrids (2-6) - August 28th, 2011 [August 28th, 2011]
- Human-Plant Hybrid (Genetic Engineering at Home) - August 28th, 2011 [August 28th, 2011]
- Ancient Alien Nephilim, Giants, Mutants, Genetic Engineering, and Hybrids (1-6) - August 29th, 2011 [August 29th, 2011]
- 3. Genetic Engineering - August 29th, 2011 [August 29th, 2011]
- Genetic engineering nightmare - August 31st, 2011 [August 31st, 2011]
- Ancient Alien Nephilim, Giants, Mutants, Genetic Engineering, and Hybrids (3-6) - August 31st, 2011 [August 31st, 2011]
- Future of genetic engineering - by Futurist Dr Patrick Dixon. Genetic mutations and genetic disorders. Gene science by conference keynote speaker - September 2nd, 2011 [September 2nd, 2011]
- Genetic engineering: The world's greatest scam? - September 3rd, 2011 [September 3rd, 2011]
- Watch Fed Up! Genetic Engineering, Industrial Agriculture and Sustainable Alternatives Full Movie Online Part 1/15 - September 3rd, 2011 [September 3rd, 2011]
- Ancient Alien Nephilim, Giants, Mutants, Genetic Engineering, and Hybrids (5-6) - September 5th, 2011 [September 5th, 2011]
- Genetic Engineering, Humans with Animals. - September 6th, 2011 [September 6th, 2011]
- Is Genetic Engineering Good for the Environment? - September 7th, 2011 [September 7th, 2011]
- Open Source Food and Genetic Engineering - Michael Pollan - September 10th, 2011 [September 10th, 2011]
- Ancient Alien ( demons ) Nephilim Giants, Mutants Genetic Engineering and Hybrids.avi - September 11th, 2011 [September 11th, 2011]
- MUST SEE : Genetic Engineering Corn Grows in Sand ! For Those That Appreciate Nature ! - September 12th, 2011 [September 12th, 2011]
- Designing Humanity - Genetic Engineering - September 14th, 2011 [September 14th, 2011]
- Genetic Modification | QUEEN ANNE SCIENCE CAFE - September 14th, 2011 [September 14th, 2011]
- Genetic Engineering in California Agriculture - September 15th, 2011 [September 15th, 2011]
- Genetic Engineering Animation - September 15th, 2011 [September 15th, 2011]
- Proof Of Ancient Genetic Engineering - September 15th, 2011 [September 15th, 2011]
- Joad Cressbeckler Fears Genetic Modification Causes 'Wrath-Minded Taters' - September 16th, 2011 [September 16th, 2011]
- Ethical Concerns With Genetic Engineering - September 16th, 2011 [September 16th, 2011]
- Scientists under Attack - Genetic Engineering in the magnetic Field of Money TRAILER - September 17th, 2011 [September 17th, 2011]
- Genetic Modification - September 18th, 2011 [September 18th, 2011]
- Genetic Engineering Not a New Science - Pamela Ronald - September 23rd, 2011 [September 23rd, 2011]
- The Island of Dr. Moreau prt. IV - September 28th, 2011 [September 28th, 2011]
- Ancient Alien Nephilim, Giants, Mutants, Genetic Engineering, and Hybrids (4-6) - September 30th, 2011 [September 30th, 2011]
- 4. Genetic Engineering (cont.) - October 2nd, 2011 [October 2nd, 2011]
- Ancient Alien Nephilim, Giants, Mutants, Genetic Engineering, and Hybrids (6-6) - October 4th, 2011 [October 4th, 2011]
- Islands at Risk (Part 3) - Genetic Engineering in Hawai'i - October 4th, 2011 [October 4th, 2011]
- Morgellons Is Genetic Engineering , A Silent Superbug - October 4th, 2011 [October 4th, 2011]
- Islands at Risk (Part 2) - Genetic Engineering in Hawai'i - October 4th, 2011 [October 4th, 2011]
- The Ethics of Genetically Engineering Children - Arthur Caplan - October 4th, 2011 [October 4th, 2011]
- Disney Geneticists Debut New Child Stars - October 4th, 2011 [October 4th, 2011]
- Genetic Engineering and Society, Lecture 1a, Honors Collegium 70A, UCLA - October 4th, 2011 [October 4th, 2011]
- OMD - Genetic Engineering (312mm Version) (Audio Only) - October 4th, 2011 [October 4th, 2011]
- The difference between normal and genetically modified food - October 4th, 2011 [October 4th, 2011]
- Bioethics Of Human Genetic Engineering - Documentary Video - October 6th, 2011 [October 6th, 2011]
- Islands at Risk (Part 1) - Genetic Engineering in Hawai'i - October 6th, 2011 [October 6th, 2011]
- Coast To Coast AM: Genetic Engineering 3-24-2011 Download Link - October 6th, 2011 [October 6th, 2011]
- Lloyd Pye - Ancient Genetic Engineering - October 13th, 2011 [October 13th, 2011]
- X RAY SPEX - ROUNDHOUSE LONDON GENETIC ENGINEERING - Video - October 13th, 2011 [October 13th, 2011]
- OMD - Genetic Engineering 1983 - Video - October 14th, 2011 [October 14th, 2011]
- OMD - GENETIC ENGINEERING - Video - October 14th, 2011 [October 14th, 2011]
- Mechanism of Recombination - Video - October 15th, 2011 [October 15th, 2011]
- Harvard Prof. Michael Sandel on Human Genetic Modification, Berkeley, CA, 7 May 2007 - Video - October 15th, 2011 [October 15th, 2011]
- Genetic Engineering [Medical Ethics Series] - (excerpt) - Video - October 15th, 2011 [October 15th, 2011]
- Genetic Engineering and Society, Lecture 1b, Honors Collegium 70A, UCLA - Video - October 24th, 2011 [October 24th, 2011]
- Genomics: genetic modification (genetic engineering) and the human gene project - Video - October 26th, 2011 [October 26th, 2011]
- Genetically Engineering Intelligent Babies - Horizon: Are We Still Evolving? Preview - BBC Two - Video - October 27th, 2011 [October 27th, 2011]
- "GENETIC ENGINEERING" GERMAN REGIME feat THIRSTIN HOWL THE3RD - Video - October 28th, 2011 [October 28th, 2011]
- Science 360: Genetic Engineering - Video - October 31st, 2011 [October 31st, 2011]
- UFOTV Presents... - Bad Seed: Danger of Genetically Modified Food - Video - November 8th, 2011 [November 8th, 2011]