I understood there are studies that say a longer delay may be better, so I'd be curious too how the result here translates to people who had a much longer time between shots. Was the UK also in this situation?
https://globalnews.ca/news/8021692/mixing-covid-19-vaccines-...
There's currently a study underway in the UK (I forget the name, but it run by the University of Oxford) to assess the efficacy of mixed-dose vaccination.
Some of the older (55+) crowd got a different mixture, with AstraZeneca shots in the early spring and Pfizer early summer.
Say what you will about our weird combos, but we have a very high number of people immunized now, so it seems to be working...
Mixed Oxford/Pfizer vaccine schedules generate robust immune response against COVID-19, finds Oxford-led study: https://www.ox.ac.uk/news/2021-06-28-mixed-oxfordpfizer-vacc... ,
.. https://science.sciencemag.org/content/373/6553/397 - "the ideal vaccination strategy may use an intramuscular vaccine to elicit a long-lived systemic IgG response and a broad repertoire of central memory B and T cells, followed by an intranasal booster that recruits memory B and T cells to the nasal passages and further guides their differentiation toward mucosal protection, including IgA secretion and tissue-resident memory cells in the respiratory tract." .. (https://news.ycombinator.com/item?id=28019151),
https://news.ycombinator.com/item?id=28016821 - Covid-19 Vaccine Intranasal Study (COV008), UK phase 1 trial recruiting,
That said, current vaccines don't provoke the exact same response as an actual infection, particularly in that they don't fully stimulate an immune response in the mucous membranes of the upper repository tract. Here's an Scientific American round-up article (from back in March): https://www.scientificamerican.com/article/to-beat-covid-we-...
[..]
The current vaccines are excellent at helping the body stop the virus as it progresses into the lungs and further (thus the massive reduction in severe illness and deaths). But it still means that there's a period of a few days after initial infection when a vaccinated person has a relatively naive immune response (while the virus is mostly just in the nose/throat). This would then result in the person still being pretty contagious. (https://news.ycombinator.com/item?id=28014448).
I would like to see intranasal Novavax (intranasal mRNA is more difficult ?), having good results, as an option to this mix..
This is still probably the most important overall point.
It seems like Pfizer had more opportunties go wrong especially when rollout was outside of hospital settings and at population scale. My understanding was initially Pfizer was limited to hospitals in Canada, but ended up in pharmacies and other temporary sites.
You mean if you then get the delta variant? Or low risk of hospitalization and death by simply getting the shot?
To be fair, you would have a low chance without any vaccinations as well. I think in the lower age brackets the risk reduction was < 10%, which is perhaps even in the range of statistical fluctuations even with large sample groups.
At least the data I saw last, cannot find it currently.
Moderna and Pfizer both have comparable (low) risk of hospitalization and death when infected with delta variant.
Primary difference vaccines is dosage (Moderna had a bit over 3x amount of material per shot) and maybe scheduling (Pfizer was scheduled for 21 days between shots, Moderna for 28 - though given how shots were actually administered in reality, this is probably a wash).
Study design has many limitations, but is probably reasonably generalizable.
As a Canadian with combo Pfizer+Moderna, I am personally curious what my risk profile would look like. I wonder if a similar study on Canadian data could be useful - an intermediate risk profile for the combo shot would sure be persuasive evidence.
Edit: Removed ambiguity in second sentence.