The previous article was all about the process of inflammation. This article is about vaccines.

The vaccines fall under the type of artificial active acquired immunity. This is artificial because we are giving the vaccine externally and this is active because the body is generating the antibodies/response and it is acquired because we are getting the immunity and it is not present by birth. You must have known what immunity is at least by now.

A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins (antigens). So these vaccines are nothing but the pathogen itself but it cannot cause any disease, instead, it triggers the immune system.

This is a quick recap of the principle of working on vaccines. The vaccine contains the pathogens as a whole or the surface antigens only. These antigens stimulate the immune system. If the immune system had a memory about this antigen, then it would immediately produce an antibody, and phagocytosis of the antigen occurs by the macrophage aided by the antibody. In this scenario, the antigen is new and there is no memory, therefore the immune system struggles and takes time to produce the antibody.

So the antigen reign over the body and this can lead to inflammation. As a result, some of the symptoms of inflammation like fever, heat, pain in the area of application, and swelling may appear. The chances of them are rare and also severity is less (last for a few hours/days) since the pathogen is attenuated.

Once the immune system produces the correct antibody, phagocytosis of the antigen occurs and hence the causative agent is eliminated from the body (primary response). So if the same or similar pathogen which has disease-causing ability enters into the body, the memory triggers the immune system to produce the correct antibody. So a heightened and rapid response is generated in order to kick away the pathogen quickly (secondary response).

There are three types of vaccines:-

Live- infection is caused without any harm – measles & polio

Dead- doesn’t last long, requires booster dose- cholera

Microbial products- involves non-infectious pathogen, capsule and toxoid- anthrax, diptheria

Hence using the vaccine as a stimulus, the body is able to generate a response that is stored and can be useful for preventing the disease caused by the pathogen.

There might be an idea to generate vaccines for all diseases so that all humans are protected. But there are some difficulties in this which are listed below:-

There are new microbes being discovered every day and no one knows which microbe can cause disease. There can be multiple microbes causing the same or similar disease. So being immune to one microbe doesn’t mean being immune to the disease

The disease-causing microbe can undergo mutation meaning that there can be changes in the genetic material and hence the antigen can change. In this case, the antibody which was stimulated by the vaccine won’t work. A suitable example is a common cold, it is impossible to produce a vaccine that covers all mutants of viruses

The pathogen has to be genetically modified so as to remove its disease-causing ability which is easy to say but difficult to implement

Also, it is important that the antigen chose for the vaccine must be close to that of the original causative agent of the disease. If the original pathogen is not so close to that of the vaccine, then it will not work

Hence all these above points explain the difficulties in producing a vaccine. Despite these many research organizations in many countries have produced vaccines especially for the pandemic and dreadful diseases like the COVID-19, hepatitis, polio, etc. in which some vaccines provide lifetime immunity to some of the diseases. We must take a minute to appreciate those who have done immense work and their contribution is stopping some of the dreadful diseases.

With this, we come to the end of the series. I hope that all the concepts explained in this were simple and clear and also would have inculcated an interest in immunology. By now, it would be clear how the immune system protects us from several microbes and diseases.