 Vaccines help a body produce immune response so that our bodies are ready to fight when they actually meet the real pathogen. These vaccines actually contain fragments of the pathogen known as antigen which our bodies can recognize and produce antibodies against them. But actually these foreign antigens present in the vaccine cannot produce a disease unlike the active pathogen. That we'll see that why these cannot produce a disease still our bodies can mount an immune response against the pathogen. Well there are various methods by which vaccines are developed. In this video we will see what are these ways and what are the vaccines approved for COVID-19 and how they work. Basically this is the structure of coronavirus which we have discussed in another video in detail. It is these surface proteins present over the coat of the virus known as spike proteins which are responsible for infection. By means of these proteins the virus attaches to receptors present on cell and then enters into the cell and after entering into the cell it actually divides and uses the cell's machinery to replicate and then the cell dies and all the virus is released into the environment which again infects other cells. So basically if our body is trained beforehand to generate an immune response against these spike proteins it can mount a very good immune response against the pathogen when it actually enters into the body. So our immune system will recognize these spike proteins and fight against it hence the virus will not be able to enter into the cells and all the events which will happen after that cannot occur. So how do we develop a vaccine against these spike proteins? Well there are broadly three methods by which vaccines are developed. First one is whole virus approach where the whole pathogen is used to introduce the body to these spike proteins. Second one is subunit approach where only these spike proteins are introduced and the third one is genetic approach which is a relatively new approach. There are currently no vaccines against any of the organisms which are developed by this approach but because of COVID-19 pandemic there are certain contenders and rather approved vaccines which have been developed using this approach. In this the genetic material which encodes for this protein is introduced into the body. Let's see each of these broad methods one by one. In whole virus approach we use the whole virus but it should not have the ability to divide inside the body remember otherwise it will cause the disease right? So we have to inactivate it. This is done by heat, chemical or radiation. In this approach basically the virus is killed and then it is reproduced and produced in large quantities. Since this is a killed virus these do not cause an infection but an immune response is generated against the proteins. The co-vaccine which is being used in India is a whole killed virion. Then another vaccine developed by China by Sinofarm which has recently been given approval by WHO for emergency use is also a killed whole virus vaccine. Another approach for using whole virus is use of live attenuated vaccine. In this the pathogen is made very weak by growing it repeatedly over cell cultures. This kind of live attenuated virus vaccine produces an infection which generates an immune response and the virus is also able to replicate a bit. But because it is a weak virus it is not able to cause a disease even though we are infected. Actually these kind of live attenuated vaccines can produce long-term immunity compared to killed virus vaccines which actually require multiple booster doses. However live attenuated vaccines are bit dangerous and need robust safety data which may take a lot of time. Also they cannot be used in immunocompromised people. Probably this is the reason that we don't have any candidate vaccine for covid in this category. Anyways there is a third subcategory in this whole virus approach. It is viral vector vaccine. In this we use some other virus as a vehicle for carrying the instructions for making proteins responsible for infection. For example the whole virus we use is a adenovirus which is a harmless virus it only causes common cold in us. So that whole virus is used and genetic material which is responsible for production of spike protein of the coronavirus is integrated with the adenovirus genome. This is known as viral vector vaccines. So virus is acting as a vehicle for carrying that particular genome into the cells so that once it enter into the cells of the body then these spike proteins can be produced and our immune system can become activated. So these vaccines are also known as a conjugate or recombinant vaccine. Covishield vaccine which is basically written like this that is a CH4 chimpanzee adenovirus oxpert one novel coronavirus vaccine is in this category. Then another sputnik B also belongs to this category. Then the vaccine developed by Janssen pharmaceutical that is ad26.Cov2.S is also of this category. Here again ad stands for adenovirus and Cov2 is for SARS Cov2 virus and finally S stands for spike proteins. Okay let's go to second broad category of vaccine that is dose developed by subunit approach. In this type of vaccine we use only very specific parts that is subunits of the virus which in this case will obviously be spike proteins. One example of this type of vaccine is Novavax COVID-19 vaccine. Again because these vaccines do not contain any pathogens they are very safe but they also do not produce long lasting immunity so for them also multiple booster doses are required. Then finally the third method of vaccine development. The third method is the newer method of vaccine development which I told that is the genetic approach. In this we actually use a part of the genetic material that provides instructions for synthesis of specific proteins. For this we can use either DNA, DNA when it enters into the cells it can be transcribed into mRNA and then which can be further translated into proteins or they can be vaccines which are mRNA based which can be directly translated into proteins upon entering into the cells of the body. The vaccines which have been developed using this approach are Moderna vaccine and Common Nati vaccine which is developed by Pfizer. So these were broad vaccine approaches which are being used for development of vaccine against COVID-19. Well thanks for watching the video if you liked it do press the like button share the video with others and do subscribe to the channel if you'd like to be open thank you.