“About a hundred people used to die from the varicella virus each year in the US. The vaccine for varicella was introduced in 1995; in a dozen years the number of deaths had been reduced to six.”
You have to use some intelligence when you look at statistics.
If you look at a graph of chickenpox cases in the US, you will see a remarkably precipitous decline starting in about 1987. From 1987 until 1995 when the vaccine was introduced the rate of infections dropped from over 200,000 to about 70,000. in the 8 years BEFORE THE VACCINE WAS INTRODUCED. The decline merely continued, maybe accelerated somewhat after then.
What caused it? Don’t know.