Earlier quoted context omitted.
Theoretically Pfizer has higher efficacy, especially with variants. Giving Pfizer to the old and AZ to the young probably saves more lives than the other way around. If you decide that you don't want to give AZ to the young any more, it doesn't follow that it's then a good idea to give it to the old, especially if you have enough supplies of Pfizer to vaccinate the old.
All the vaccines have 100% efficacy in preventing ICU admissions so far.
>Hospitalization data for 129 of the fully vaccinated cases is incomplete, Sutfin said. But for the 117 people for whom hospitalization records are known, 11 were hospitalized.
https://www.freep.com/story/news/local/michigan/2021/04/06/v...
"However, since February 1, eight people with vaccine breakthrough have been hospitalized. DOH is investigating two potential vaccine breakthrough cases where the patients died."
https://www.doh.wa.gov/Newsroom/Articles/ID/2720/Cases-of-CO...