COVID19 Vaccines – Mechanism of action
Ever since the beginning of COVID19 pandemic health professionals and scientists along with pharma giants have been working on developing COVID19 vaccines. After almost a year long battle against COVID19, ray of hope has emerged as countries around world have succeeded in clinical trials of vaccine. With 64 vaccine candidates in clinical developmental stage and 173 vaccine candidates in preclinical stage (as per data from WHO) scientific community has done remarkable achievement. Different targets and platforms are used for design and development of vaccine candidates. The current article shall give an overview on few approved COVID19 vaccine candidates and their mechanism of action.
Target for COVID19 vaccines
The four types of structural proteins present in COVID19 virus are spike protein (S), envelope protein (E), membrane glycoprotein (M) and nucleocapsid protein (N). Researches have demonstrated that S protein is a prime target for the designing and developing vaccines. S protein responsible for the attachment of virus to the host’s cell surface receptor. Antibodies targeting the S protein of SARS-CoV-2 can interfere with the virus resulting in neutralization of the infection caused by the virus. The major target antigen is S protein for most of the platforms except the conventional ones (Live attenuated and Inactivated vaccines) where the whole virion or subunit is used to develop vaccines.
Mechanism of action COVID19 vaccines
mRNA based COVID19 vaccines
- A new type of vaccine to protect against infectious diseases.
- They guide our cells how to make a protein or even just a piece of a protein which triggers an immune response in the body. The immune response, which produces antibodies, protects the individual from getting infected if the real virus enters the body.
- In this manner COVID19 mRNA vaccines guides cells of our body to make a harmless piece of “spike protein.” The spike protein is found on the surface of the virus that causes COVID19.
- After the body cells make copies of the protein, they destroy the genetic material from the vaccine.
- Further body recognizes that the protein should be eliminated and builds T-lymphocytes and B-lymphocytes (defense cells) which will remember how to fight the virus that causes COVID19 if infected in the future.
- Examples: Moderna, Pfizer
Vector based COVID19 vaccines
- Contains a weakened version of a live virus i.e., a different virus from that causes COVID19.
- It will have genetic material from the virus that causes COVID19 inserted in it (this is called a viral vector).
- After the viral vector is injected into human body, the genetic material gives instructions to cells to make a protein that is unique to the virus that causes COVID19.
- Using these instructions, human body cells make copies of the protein which in turn prompts the body to build T-lymphocytes and B-lymphocytes (defense cells) that will remember how to fight that virus if infected in the future.
- This type of platform has better safe track record
- Example: COVISHIELD™ [ChAdOx1 nCoV- 19 Corona Virus Vaccine (Recombinant)]
Inactivated COVID19 vaccines
- One of the oldest methods of viral vaccination
- This is the way the flu and polio vaccines are made – and vaccines can be manufactured on a reasonable scale.
- It involves isolating and inactivating the virus; Even though the pathogen is dead, the immune system can still learn from its antigens how to fight live versions of it in the future.
- Example: COVAXIN™
There are other platforms and mechanism on which COVID19 vaccines are being developed, namely DNA based vaccine, Live –attenuated vaccine, Non- replicating viral vector vaccine, Plant based adjuvant and so on. All these are in different phases of clinical trial and complete data are yet to be published.
In the COVID19 vaccine race, a few vaccine candidates are already approved for use and are being utilized for vaccination. There are several others in various stages of clinical trials. So far commendable job has been done by scientists and health workers. Although vaccine is a ray of hope, masks and social distancing, help reduce your chance of being exposed to the virus or spreading it to others. Getting vaccinated is one of many steps we can take to protect ourselves and others from COVID19.