Until about 200 years ago, people did not understand the cause of disease. In olden times, people thought that evil spirits caused disease. Then it was ‘bad air’ also called a ‘miasma’. (Malaria has been, and continues to be a major cause of human disease, disability and death. It means coming form ‘ bad air”)
With the microscope, we discovered bacteria and other ‘micro-organisms’. A virus is so small, that it cannot be seen in a microscope, but its effects on cells can be. And with special microscopes that use X-rays instead of visible light, we can now take pictures of viruses. And now we understand that not only infectious diseases, but cancer and perhaps have these tiny germs as the cause of much human disease.
This germ theory of disease has enabled interventions like vaccines and antibiotics; clean water and sewerage systems; housing standards that been very instrumental at improving human life spans from around 30-40 years to over 80 years today, for the best countries.
Why are vaccines so controversial, then?
Because of a cognitive bias: a problem with our ‘natural’ way of thinking. This bias was described by the ancients – the fallacy of Post hoc, ergo proper hoc: If an event happens after ‘hoc’ (a thing), so it was caused by that thing. This is because our brains are designed to find patterns where none exist, so that we do not miss potential associations. This is why we need statistics. But also structured logic to make sure that cause and effect are correctly understood (“Correlation is not causation”).
Since, nearly every child will have a vaccine, it is inevitable that serious and sometimes fatal events will happen after vaccine. Vaccines are supposed to generate a reaction in the body. Symptoms from such reactions may blur with a coincidental disease process, leading to even more conviction that it was the vaccine that caused the disease; even when it is ‘coincidental’. Which just means that the two events (vaccine and problem), just happened to be at that time, and really unrelated to each other.
For example, the other day I had my influenza vaccine. The next day, I slipped while walking on some steps in heavy rain with obstructed vision. Could the vaccine have affected my balance, and be to blame? The only way to know for certain is to do controlled studies when we can compare rates of events. Many people have told me that when they get influenza vaccine, they get sick with influenza. Well you can get some the symptoms of influenza infection from the vaccine; and that may be the explanation for some. More likely, they just happened to get infected with one of the many viruses that causes an ‘influenza-like illness’. And we know this because when we do controlled studies we see these vaccine reactions, but no increase in other infections between vaccinated and non-vaccinated.
Science is unable to ‘prove’ anything. At best, we have working models that describe the world well. We know, that sometimes these can work, even when they are wrong. And the Universe seems to require paradoxical truths: light is both particle and wave.