A human body comprises over 30 trillion (1 Trillion = 1012) cells, divided into about 200 cell categories, e.g., skin cells, stem cells, muscle cells, etc.
And because it is an attractive place (full of nutrition) for pathogens (virus, bacteria, etc.), the body is always at risk of invasion by these foreign objects.
To control this invasion, the body deploys over 20 billion (1 billion = 109) leukocytes (white blood cells – a key component in our blood) that roam around the body like security personnel.
But since the cell population is vast, it could be difficult for leukocytes to identify any invaders (bacteria, virus, etc.) that move in secretly.
So, the body has given tags to every cell that belongs to the body.
These tags or markers are called antigens, and they read something like: “My name is a skin cell, and I am not an invader.”
The leukocytes keep monitoring all the cells in the body, and the moment they sense anything whose tag doesn’t seem valid, they call the armed forces of the body (B-cells & T-cells) and give them the tag details of this pathogen.
B-cells & T-cells produce customised antibodies (soldiers) that exactly match the pathogen tags and get attached to each pathogen like a key in the lock and kill all of them.
The beauty of the human body is that once it produces antibodies against a pathogen, it also creates antibody-producing memory cells that live long and always remember the pathogens and the required actions.
Vaccines work on this memory aspect of our immune system—they contain killed or weakened versions of the virus or a small part of it, such as a protein or nucleic acid.
When we get a vaccine, our immune system recognises the virus as foreign and creates antibodies and memory cells that protect us against future infections.
Now, in the COVID vaccine’s effectiveness studies, it was found that the antibodies produced in the body by a given dose were far less than antibodies that were present in the bodies of those who had survived the COVID infection.
And when the 2nd dose was given, the level of antibodies increased dramatically.
So, the vaccine was created to work on the “prime and boost” strategy—similar to painting a wall that hasn’t had paint on it before.
The first dose helps to prime your immune system, and the second dose—if given after a certain time—boosts the response (as confirmed by trials).
Like you need to get the primer to dry before painting, the 2nd dose needs to be taken after a certain time, otherwise, its effectiveness is impacted.
However, delaying the dose even by 45 weeks has been found to have no impact on the effectiveness.
