My dad got covid few days he had his first dose of vaccine. Do you know anyone who experienced this?

On the 15th day since he got his 1st dose of covid vaccine signs and symptoms of covid started to show. He is a senior 74 years of age, with comorbidities and has Alzheimer's disease. After almost 2 weeks of hospitalization now he's home for his recovery. Thank you Lord that he is improving he still need O2 for a month to complete his recovery. Once he is fully recovered he can still get the 2nd dose of vaccine for full protection. It is very important to complete the number of vaccine doses for complete and full protection from Covid.