Reluctantly, I feel I need to clarify some issues around why AZ doesn't make sense for most of Canada right now.

When NACI evaluated—using the hard endpoint of deaths—the risk-benefit of AZ vs. no AZ, it used a lower incidence 1 per 100 000.

With this modeling, it makes clear sense to give AZ vs. waiting for age 50-69 in a moderate incidence setting, and for all ages in high incidence setting.

But what happens if the VITT rate is 1:26 000 or 3.85/100 000? You get this ...

This means that it is only a slam dunk (vs. no vaccine) for age 50+ in high incidence (30 cases/100K/day) settings, and 40+ in very high incidence (60 cases/100K/day) settings. Even if VITT incidence is 1:40 000 (or 2.5/100K/day), your expected VITT deaths/100K are 0.63-1.0.

This alone makes AZ vs. waiting a challenging choice. But it isn't AZ vs. no AZ. We have enough mRNA in Canada to replace the very small AZ remaining. We have had 2.3M AZ delivered to Canada. As of May 1, 1.55M have been administered, leaving us with no more than ~600K doses.

Those AZ doses will predictably lead to 5-23 deaths, and many more cases of severe illness. It only makes sense to give it to people at those very high risks of disease. But why give them AZ, when we can give them an mRNA vax (which we're getting >2M/wk now)? @imgrund

Also, the projected wait time for mRNA is ~0 for age 60-69, 1 week for 50-59, and 2 weeks for 40-49. at the moment. This is incredibly short, and the onus should be on provinces and their vaccine task forces to get mRNA to the highest risk populations.

I want to emphasize again—because it seemed to be overlooked in my original thread—if you cannot get mRNA to the very high risk, then AZ likely makes sense over no vaccine. Without question. Several ( @TerryWuerz @AntibioticDoc) have pointed out disease dynamics in AB & MB.

Others have questioned what happens to the 1.55M who have received a single dose of AZ. We don't know for sure: Risk of VITT in second doses is unknown but not zero. Almost certainly they will just need a single dose of an alternative (i.e. mRNA) vaccine. Maybe a second jab.

AZ was a good vaccine that served its purpose. They are meant to protect >> result in harm. We have options.

I have tried to be very transparent with all numbers.
Vax admin: https://health-infobase.canada.ca/covid-19/vaccination-coverage/#a6
NACI report (see ~p. 110): https://www.canada.ca/content/dam/phac-aspc/documents/services/immunization/national-advisory-committee-on-immunization-naci/recommendations-use-covid-19-vaccines/recommendations-use-covid-19-vaccines-en.pdf