A predictable outcome of mass vaccination in the middle of a pandemic (particularly when the vaccine being distributed only provides immunity to one specific feature of the virus) is the emergence of variants that succeed in populations with high vaccination rates.
"Our modeling suggests that SARS-CoV-2 mutants with one or two mildly deleterious mutations are expected to exist in high numbers due to neutral genetic variation, and consequently resistance to vaccines or other prophylactics that rely on one or two antibodies for protection can develop quickly -and repeatedly- under positive selection."
Risk of rapid evolutionary escape from biomedical interventions targeting SARS-CoV-2 spike protein