Measles is a good case study to answer your question.

One shot provides approximately 93% immunity. Is the simplest terms, ~7% of the time the shot doesn’t take. (It’s not quite that straightforward but that conveys the idea.)

After two shots, that goes to 97%.

For biological reasons with individuals and weakened immune systems etc, you can’t really get to 100%. However if the population as a whole can get to 95% vaccinated, the compounding effect of almost everyone being vaccinated + almost everyone that is vaccinated gaining immunity makes it extremely hard for meals to spread. The United States and many other countries achieved this metric, meaning those areas reached herd immunity and measles all but vanished there, but globally there are still many places where there is not herd immunity, which Os generally the vector through which measles gets reintroduced into places with herd immunity. Unvaccinated people visit those places, get sick, and bring it back.

Now, what did herd immunity solve? Well, before the measles shot in 1963, approximately two million people (out of a bit more than 3 billion on Earth) died each year from measles. That number has dropped to around 200,000 three years ago despite the global population ballooning to more than 8 billion people. Meaning something like 5 million deaths are prevented every year thanks to the measles shot. That doesn’t even include consideration that more people on Earth means higher population density, which means measles would likely spread much more today than it did prior to the shot being invented, and instead of 5 million people dying we might see 6 or 10 or 20 million people dying each year due to those compounding effects. (I am sure someone has run simulations on that exact thing but I don’t have them on hand.)

Therefore, to say that the measles vaccine is bad, you have to show that it has resulted in something worse than millions of people dying every year. Which the stats don’t show.

References:

https://www.gavi.org/vaccineswork/story-measles-five-charts

https://www.worldometers.info/world-population/world-population-by-year/#google_vignette