Edward Jenner vaccinating patients against smallpox (CC BY 4.0)
Vaccine is a word that derives from a Latin word ‘vacca’ meaning cow. Why would such an important tool in times like these have any relation to the cow?
Well, in 1796, a local milkmaid in Berkeley contracted cowpox and went to a local doctor named Edward Jenner. During the treatment, Jenner came to understand that infection with cowpox, whose symptoms were quite mild as compared to smallpox, could serve as an antidote to smallpox as well.
Jenner took a small amount of extract from the milkmaid’s cowpox lesion and inoculated it into another subject who did not have smallpox. The subject later was injected with smallpox taken from another patient who was actively infected with the disease. But this time, interestingly the subject was immune to smallpox and did not develop any symptoms. This is because the body had developed antibodies against cowpox and these were effective against smallpox too.
Now, before we engage ourselves in exploring how the novel Coronavirus vaccine works, we need to understand and know, how the body’s immune system responds when it is exposed to any pathogen.
There are mainly two types of immune systems. One, being the innate immune system which the body is born with and secondly, the adaptive immune system which is continuously evolving as the body is exposed to different pathogens and their products.
The innate immune system is the body’s first responder and it helps in killing the invading pathogens. This process is also known as phagocytosis, deriving its name from the innate immune system cells phagocytes. The adaptive immunity involves developing new antibodies every time the body gets exposed to a new pathogen. The antibodies developed are developed by cells called B-lymphocytes.
So now, let’s know about the mechanism of the adaptive immune system and how it responds once it is exposed to a pathogen. The first line of warriors is comprised of the immune cells called macrophages which will phagocytose or kill the invading organism. In this process, certain products called ‘antigens’ (antibody generations) are released which are then passed on to lymphocytes via dendritic cells.
The Lymphocytes enclose cells called T-cells and B-cells which form the basis of the adaptive immunity. T-cells are specifically activated against the invading organism and thus help to eliminate it while the B-cells will form antibodies against the antigen. Memory cells are also formed which will respond in case of a subsequent invasion by the same organism.
So now, we have a rather complicated and robust immune system, but why can’t it fight an apparently harmless virus like the common cold? This is because every bout of common cold involves a newly mutated virus with new antigens on which the previous antibodies developed don’t work.
What about other viruses? The viruses, which even mutate! We develop vaccines to produce adaptive immunity against these viruses so that you don’t have to go through the symptoms of the disease every time you get exposed to a particular virus.
2020 was a rather woeful year for the world. The Coronavirus pandemic gripped the globe. In India, the number of the affected was more than 10.6 million out of which 153 thousand died. India has procured two vaccines against the SARS-CoV-2. The first one was developed by Oxford-AstraZeneca also named as Covishield. The second vaccine is being indigenously developed by Bharat Biotech in collaboration with Indian Council of Medical Research (ICMR) called BBV152/Covaxin.
Both the vaccines induce an immune response but the difference is in the key ingredients which initiate the mechanism of adaptive immunity.
The Covishield vaccine contains a piece of the virus which is a protein protruding like a spike from the surface of the virus. Once injected into the body, this protein will multiply and produce several copies of itself, enough to elicit an immune response in the form of antibodies against it. The protein needs a vehicle; here, the vehicle is a vector used to sustain itself in the human cell. This vector in Covishield is a weakened adenovirus found in Chimpanzees which by itself cannot cause any infection.
As compared to the Covishield vaccine, the Covaxin contains the entire Coronavirus but in an inactivated form which would evoke a protective immune response again in the form of antibodies.
Nikhil Jaisinghani is a Master's student at Leibniz University, Hannover, Germany.
(The views of the author in the blog are personal and these views do not necessarily represent the views of Science Reporter)