Where exactly do you get the 1.7%? Is it computed the same way the breakthrough deaths are computed? What is the denominator in each case?
I see, you are using this table[1] ... This is the case fatality rate (which is inflated depending on how many infections are never recorded).
Using the numbers provided by the CDC, if we put the cases in the denominator and not the vaccinated population, we have:
Hospitalized or fatal vaccine breakthrough cases reported to CDC 8,054
Deaths† 1,587
†341 (21%) of 1,587 fatal cases reported as asymptomatic or not related to COVID-19.
Now, if the CDC had not stopped reporting the number of infections, we'd have the correct comparison. If we take cases as the cases reported by CDC, we have (1,587 - 341)/8,054 = 15.5% of the cases resulting in death from Covid19 of a person who is fully vaccinated against Covid19.
Why did the CDC stop reporting total breakthrough infections (which would have allowed an apples to apples comparison of CFR here)?
[1]: https://coronavirus.jhu.edu/data/mortality