Well, this is rather interesting... https://sebastianrushworth.com/2021/11/05/covid-how-long-does-vaccine-based-immunity-last/
The recent paper from Qatar was interesting.
Now, that had similar estimates of vaccine effectiveness to the Sweden paper. However it, like the Sweden paper, used Test-Negative Case Control at the method. This is a great method, but it has a few potential 'gotchas' that can result in an overestimate of vaccine effectiveness -- I believe that this has occurred.
The Qatar paper was interesting because buried in the detail were two pieces of information that overcome the weakness in the TNCC method.
The first was that they measured effectiveness at preventing asymptomatic infection. This was rather negative. The official presumption is that they're just really bad at protecting against asymptomatic infection, but I'd suggest that it is easier to believe that this is just overcoming the problem with TNCC.
The other useful bit of information was that they did a multivariate analysis as well as the TNCC. This also showed very negative vaccine effectiveness. TNCC is used because it is cheap and fast, not because it gives different results to other methods. If TNCC is giving a vastly different answer than multivariate analysis that suggests that something has gone wrong in the analysis, not that TNCC is best and you can ignore the rest.
The Qatar paper got published in the NEJM with slightly different data and findings to the preprint.
https://www.nejm.org/doi/10.1056/NEJMoa2114114
VE against infection wanes relatively slowly for 4 months or so then drops much more rapidly (it halves) in a month.
At T=5 months its showing 17% and 6 months 22%. Ultimately it looks like this will be the long term background plateau.
Either way its poor (although against severe illness it held up far far better).
The results do agree with the Israeli study showing 20% or so VEs 5 months on.
PHE and ONS from the UK do rank it higher but different methodology.
Ultimately though all the data shows its decent for 4 months then drops off rapidly after that to become near useless 6 months on.
Astrazenica is consistently 20% VE lower than Pfizer for all time periods.
Be wary of older studies that included a lot of Alpha cases - forget that. Delta is the only game in town now.
