Your doctor friends were informing you about a phenomenon commonly referred to as "immune escape".
The current mRNA based SARS-CoV-2 vaccines are effective at preventing severe outcomes like hospitalization and death. However, they do not necessarily prevent infection or transmission - and they induce an immune response highly targeted toward the spike protein RBD [1]. Combined with mass vaccination strategies, these factors contribute to a situation that exerts tremendous selective pressure on the virus, and can result in convergent mutations that are advantageous for the virus in a large population of people [1][2]. These mutations can lead to partial or complete immune escape, which manifests as increased transmission or virulence, reduced vaccine efficacy, and reduced immunity in naturally infected individuals.
> Even the highest levels of vaccination are no protection
It's not quite accurate to say "are no protection". I would rephrase as:
Strategies for viral elimination should therefore be diversified across molecular targets and therapeutic modalities [1]
[1] Risk of rapid evolutionary escape from biomedical interventions targeting SARS-CoV-2 spike protein https://pubmed.ncbi.nlm.nih.gov/33909660/
[2] SARS-CoV-2 immune evasion by the B.1.427/B.1.429 variant of concern https://science.sciencemag.org/content/early/2021/06/30/scie...