https://en.wikipedia.org/wiki/Cutter_Laboratories#Cutter_incident
Not going to bother with working out percentages, but a defective vaccine causing 40,000 cases of disease is not insignificant.
No dog in this fight, just wanted to throw that out there since there was a query.
This can't be used as an example and I will explain some of it, and trust you will do due diligence to convince yourself, learn the details, and understand that this can not possibly be representative of all vaccine.
There are complicated reasons why the two polio vaccines, in particular, have issues that other vaccines would not, and it has to do with, on the one hand, one polio vaccine containing live polio virus and the other containing dead polio virus, and on the other hand, what level of advancement the regional society is where vaccinations being given. The vaccine containing live virus is more dangerous, yet it must be used in Third World countries at risk of outbreak or epidemic, while in First and Second World countries, the vaccine containing the dead polio virus is sufficient and more ideal. I believe it possibly has something to do with a booster shot for the vaccine with dead polio virus that needs to happen at a certain time, after 4 months, and this is unlikely to be applied in Third World countries, where individuals may not have an actual address even if they live somewhere, nor identification. The polio vaccine with the live virus does not need that booster.
I hesitate to say more because in the details I will get tripped up, but that should be enough for any to find the reasons for my first statement above, that this can not be used as an example of a general case for vaccines, because it could only be true of polio vaccines in our world of variable levels of technology, economics, and closely linked, sanitation and health care.
You can not apply this to any other vaccine as some example that, "whoa, we gotta be careful with this because of how wrong this can go," and suggesting so could would spread this false idea, causing reluctance to vaccinations. The damage that Jenny McCarthy has done is unknowable, but it is significant. We don't want that. Nothing like this could possibly happen with any of the SARS-CoV-2 vaccines, nor any other vaccine, such as measles. What is assured is that not getting vaccinated for such things as measles
causes unnecessary outbreaks. With the SARS-CoV-2 vaccines, when available, it is a no brainer that everyone should be vaccinated, and there is no cause to democratize this among those without scientific or biological education to weigh the risks. It makes best sense to get vaccinated as soon as possible, and if enough percentage get vaccinated, herd immunity will kick in for those that for whatever reasons did not get vaccinated. 50% won't get it done. Most need to get vaccinated for herd immunity to materialize.