Herd immunity is a scientific fact. You just misunderstood the concept. If you are not immune, but everyone around you is, then you cannot contract the disease because you will not be exposed to it. You don't become immune.
You will not be exposed to a disease only if you remain within that group. Given the constant return to ‘their’ country by the ‘immigrants’ how likely is it that they will remain within their group of the immunized.
Highly unlikely, IMHO.
Herd immunity works to a certain extent. However, there is a risk for the vaccinated from the unvaccinated, because no vaccine is always, everywhere 100% effective. So, even if you are responsible and have your children vaccinated, they might still be infected by an unvaccinated child whose parents are not responsible and have fallen for the anti-vaccine propaganda promulgated by quack doctors and idiot celebrities.
One is safer being an unvaccinated person in a herd of vaccinated people than one is being a vaccinated person in a herd of unvaccinated people. Ironic, isn’t it?
When a large epidemic of pertussis hits, people will be lining up to have their children vaccinated. Too bad it will have to go that far before people realize they are being foolish.