I know only one vaccine that might have 100% efficacy after 4 shots. It is polio vaccine.

COVID-19 has been so far a scourge - when we get enough people vaccinated in developed countries, another variant appears from developing countries. The vaccine deployments has been just too slow around the world.

My hope is that the developing world has seen now enough of the virus and is mainly immune or will be after Omicron has swept over (being hopefully milder than previous variants).