As mentioned in a previous post, Canada has approved the Oxford vaccine. This story some interesting details which I will summarise here.
Health Canada approves AstraZeneca's COVID-19 vaccine
The first thing to note is that two suppliers have been approved, both AstraZeneca and the Serum Institute of India (SII), the latter being the world's largest vaccine maker who are supplying a large part of the world demand for the Oxford vaccine.
The first shipment of 500,000 doses from SII will arrive next Wednesday.
The more important discussion concerns "efficacy" numbers. There are several videos in the article in which Health Canada experts explain why the numbers for different vaccines can't really be compared to one another. In a previous post I mentioned that they were tested in different places at different times against different mixtures of virus variants.
Dr. Supriya Sharma also explained that the trials were constructed in different ways, with different criteria, run for different lengths of time, and had different end points. There were no head-to-head comparisons done which measured all the vaccines in the same way against the same standard. All of this together means that there is no way to reliably compare the vaccines to one another in terms of a simple "efficacy" number. All the efficacy number can tell you is that if it is reasonably high enough, then we know the vaccine is effective. Dr. Supriya Sharma pointed out that in the trial data, none of the people vaccinated with any of the vaccines being considered including the Oxford vaccine died of COVID-19, or were hospitalised with the disease.
Dr. Supriya Sharma also addressed the question of efficacy of the Oxford vaccine among older people. She said there was nothing in the trials which suggested that it wouldn't be effective in older people, the issue was simply the limited number of older people in the trial limited the amount of data available in that age group. However, she said that real world experience with the Oxford vaccine, including the study done in Scotland, provided pretty convincing evidence that the Oxford vaccine was just as effective among older people as it was with younger age groups.
Another health expert noted that the Oxford vaccine was a fairly conventional type and that anyone with experience with vaccines would expect it to be effective in older age groups based on the way that it works.
Health Canada are recommending that the Oxford vaccine be given in two doses 4 to 12 weeks apart, and Dr. Sharma said that current evidence that waiting the full 12 weeks before giving the second dose will increase its effectiveness.