This isn’t unexpected. The vaccines don’t stop you getting infected. They are meant to stop you getting so sick that you end up in hospital.
So the point here is that those people don’t end up in hospital, they just get mild or moderate symptoms then get better.
It’s important that everyone understands that.
Which is why, even after getting vaccinated, we all still adhere to distancing and hand hygiene, until everyone is vaccinated – because even if you have a mild case, you might give it to someone who isn’t vaccinated yet and they end up in hospital.