Yes, vaccines are very effective in tackling infectious diseases. Vaccine works by creating a memory about the pathogen and neutralizing it when it encounters the same pathogen again.
We will jump into more detail, but in a very simplified way. All figures quoted are approx, just give the extent of efficiency. Every virus, every lymphocyte behaves differently.
To understand how vaccines work, we need to understand how the body fights any pathogens. When the body is invaded by a pathogen, the body deploys first level defence innate immune cells. In most cases it is sufficient, but in some cases it is not and when the adaptive immune system kicks in (lymphocytes). If it is the first time then lymphocytes have to learn about pathogens and develop an antibody response which helps in tackling the pathogens. This counter attack is very precise and it targets pathogens like a guided missile. Since they have never seen the pathogen before, this process takes a while or the person may even die, before lymphocytes find the antibody. Once they encounter the pathogen, they also make memory of pathogens. If the pathogens come again, then lymphocytes, identify the pathogen faster and activate sooner, lot faster, let stay 10times or more .
Now here is where the vaccine comes into play. Vaccines are nothing but weakened pathogens, or it could be any part of pathogens (antigens). Once a vaccine is administered, the body undergoes the exact same response as detailed above. Weakened viruses (or just portions of virus) never could replicate, and hence a significantly large dose is given, so as to create lymphocytes response and creation of memory lymphocytes. Some cases multiple doses are required. If an actual virus invades the body, memory lymphocytes will get activated a lot faster and virus neutralized without even the patient knowing it. If we assume the virus kills 10%, then every 1000, 100 patients will die. Normally with a vaccine not a single patient would die in such a case, max may be 1 will get some adverse reaction. Vaccines are 99.99% effective in saving lives or preventing disability like polio virus.
There are many advantages about vaccines even if viruses don't kill the patient, sometimes the body does take time to produce a response and real viruses will destroy the body before that (example polio). There are also cases like coronavirus, where virus multiples and our own lymphocytes restore to nuking to kill the virus (cytokine storm), which do severe damages to lungs of humans and this is the main reason why humans are dying from coronavirus or even common flu. With a vaccine body will be trained in recognizing the virus and such eventuality will never arise. Also vaccines help us wipe out viruses completely, even if the death rate is less, as it can mutate anytime to become more dangerous or contagious. Also vaccine prevent random damages to body caused by virus, take example coronavirus, it can damages 1000+ place in body as it capable to bind to many places in body. Sometimes it leads to other diseases, cancer or life long problems. Sometimes the virus makes its way to the brain, eyes, nerves etc, which is out of reach for lymphocytes and can live there for a long long time. There are cases in coronavirus, where patients never get well, sometimes get sick, get better and get sick again.
It is never too late to take a vaccine, make sure to take your vaccine now. Also it is advisable to take every vaccine available as soon as it is available.
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