On the other hand:
Sieben junge Deutsche infizieren sich in Südafrika trotz Dritt-Impfung
Short english summary: 7 germans on a trip through South Africa all catched Omikron. All 7 of them were fully vaccinated and boostered:
1-5: 2xPfizer + Pfizer Booster
6: 2x Pfizer + Moderna Booster
7: 1x Astra / 1x Pfizer + Pfizer Booster
They got their booster between 5-10 month after their second initial shot and all of them were boostered between 1-2 month ago as of the the time they catched their breakthrough infections (among the earliest people in Germany to receive boosters)
Wolfgang Preiser from Stellenbosch University near Kapstadt, member of the team that identified Ominkron told the Tagesspiegel:
"We're currently seeing a lot of breakthrough infections. What we did not know is that even a booster mit Pfizer does not prevent it"
Original:
„Durchbruchsinfektionen sehen wir gerade sehr viele. Was wir nicht wussten ist, dass auch eine Booster-Impfung mit Biontech/Pfizer das nicht verhindert“, erklärte Preiser gegenüber dem Tagesspiegel.