That’s not how herd immunity works, once the population reaches a certain threshold it all goes to the toilet because not everybody can sustain the same immunity over long periods of time.

Herd immunity makes it hard for the virus to jump from person to person because the statistics dictate how likely it is for transmission to occur.

When a large amount of people are immunized it is less likely for it to jump from a newly vaccinated child to an adult that got vaccinated years ago because of the buffers that might exist in between those people.

When a less than useful amount of people are vaccinated it is more likely that it will just jump to all of the adults with weaker immunity.

So even if you’re immunized, sometimes that immunity goes away quickly as it did with the COVID vaccine.

Humanity is reaping what they sowed.

The problem is that the voluntarily unvaccinated give the disease the chance to circulate. Once in circulation it will harm some people who are vaccinated and some people who can't be vaccinated. Vaccination is in part an altruistic act that helps protect others. But antivaxers don't seem to understand this notion of doing something to protect other people.