Grateful for the hard work of dedicated public health scientists at @PHE_uk like @kallmemeg and unsung others who work overtime to produce excellent reports on the variant of concern B1.617.2 🇮🇳
🧵analysis of vax effectiveness, and why interpretation of reduced VE limited.
1/
PHE did a 'test negative case control study' w/ logistic regression as I outlined yday.
From test and vax databases they retrospectively created a control cohort of 99k who tested negative and compared to 6.4k test positive for B117 & 1k for B1.617.2
The longer it takes to statistically tell difference between vax effectiveness against variants the smaller the actual dip (if any) in protection will be.
In randomised control trials we can be confident in vax effect after only 100+ infections because selection bias and confounding variables between the vaxxed and unvaxxed comparison populations are (e)limited by the randomisation process.
2/
This is not the case when we do retrospective observational studies - like vax effectiveness against variants in the field.
The statistical analysis is more challenging. There are biases in who is vaxxed or infected, living, working, mixing patterns, medical health/immunity.
3/
We kept seeing 1 dose vax after prior infxn boosting Ab tires 3X higher than 2 doses at the standard 3 week interval. Some of us wondered if this was from optimised prime-boost interval at the time...
Fantasy commentary letter in Lancet (not a peer reviewed study)!
It's an unreasonable proposition for most countries like the UK to achieve elimination + constraints of reality negates claimed economic and liberty benefits if attempted...