In breakthrough cases where the individual has a high viral load and typical COVID symptoms (shortness of breath, fatigue, etc.) it's not unreasonable to assume that the person might suffer from the same course of illness as an unvaccinated person. While the vaccines clearly reduce the incidence of hospitalization and death, there are people whose breakthrough cases aren't exactly what the average person would call "mild".
https://www.nejm.org/doi/full/10.1056/NEJMoa2109072
In breakthrough cases where the individual has a high viral load and typical COVID symptoms (shortness of breath, fatigue, etc.) it's not unreasonable to assume that the person might suffer from the same course of illness as an unvaccinated person. While the vaccines clearly reduce the incidence of hospitalization and death, there are people whose breakthrough cases aren't exactly what the average person would call "mild".