Herd immunity has nothing to do with genetics
An immunity not created through a vaccine or introduction of a disease to trigger an immune response is called INNATE IMMUNITY, or natural immunity.
An example in humans would be our skin. It protects our highly sensitive nervous system from pathogens that already have access to our bodies. They are kept from infecting the internal structures and organs. Clotting of blood is another example. If the skin is damaged, the blood clots to seal the wound against infections. These are mechanisms that have evolved in vertebrates to actually make us immune from the pathological agents in our environment.
Every germ-fighting mechanism in our bodies has evolved over time to compensate for "design flaws" that proved to be vulnerable to infections. We often say "immune" when in reality we should say, "infection fighting mechanisms," because they only act when a specific pathogen is detected in the body -- i.e. you're already infected, but your body is taking care of it.
When fighting a new virus, unless it acts nearly identical to another infection which our bodies already recognize, the body uses the adaptive immune system, aka the acquired immune system. This is what most people understand as immunity, because most vaccines are designed to trigger these immunity responses in our bodies. Once the antibodies are created, they provide some degree of immunity for some amount of time.
Acquired immunity creates immunological memory after an initial response to a specific pathogen, and leads to an enhanced response to subsequent encounters with that pathogen. It's more specific to a pathogen than innate immunity.
Acquired immunity normally does not prevent infections, but rather it provides an ENHANCED RESPONSE to an infection. The body has been "taught" how to fight a specific pathogen, and it can produce the appropriate antibodies in response.
So, SCIENCE tells us that EVEN IF you have been vaccinated or infected in the past, you are not technically immune from reinfection. The body, however, has been prepared with a blueprint on how to fight the infection by virtue of seeing the pathogen before.
In short (too late?), we can have immunity from COVID-19 and still get reinfected. Reinfection rates, therefore, are irrelevant.
If you need an example of this, look up chicken pox and reinfections in older adults (shingles). Even though we all have been immunized against chicken pox, either through infection or vaccination, the immunity is created from the live virus. Shingles occur when the virus in the body reactivates -- normally decades after childhood infection.
Arguing over reinfection probabilities and rates is pointless.