No it isn’t, we have decades of hard data showing what it takes.
You start getting some benefit around 40%, but you don’t have full herd immunity until reaching the 85-95% threshold.
That is why even a handful of anti vaxxer lunatics risk widespread resurgence of diseases we thought we had “cured”.
Vaccines are not 100% effective, at best they are generally 75-85% effective at preventing those vaccinated from ever reaching a high enough level of infection to either become clinically ill themselves or to spread the disease.
Thus we’re already starting out well below 100% protection even with 100% vaccination.
The same is true with actual exposure to these diseases, not everyone will develop strong immunity to the disease after being exposed.
One way or another you have to reach that 85-95% threshold to stop the spread of viral contagions or else put everyone into long term absolute quarantines except for those deemed most vital to keeping the rest alive.