Indeed, and this is seen with everything. It’s the entire reason we see some most people surviving COVID-19 with mild symptoms or no symptoms at all, while 0.65 - 1% of people die from it: differences in the immune system. Even with vaccination, nothing is ever certain. But we don’t need a perfect vaccine to achieve a perfect result. The smallpox vaccine is 95% effective. That imperfect vaccine wiped smallpox off the face of the Earth. The last case documented was in 1978. The vaccine was so effective, we don’t even vaccinate against it anymore.
I see the vaccine like I see a oil filter. Oil laden with oxidated metal flow through the filter and not all of it is caught by the filter. However, as the oil circulates through the system, it continuously enters the filter over and over. Each time the oil is cleansed of more impurities. In the case of the virus, it goes through the human immune system. Those who have their immune system enhanced with immunity (from infection or vaccine) will “filter” out the virus. Those without immunity will allow the virus out into the system to be caught, perhaps, by those with immunity. This cycle will eventually cleanse the population of the virus.