70% [68,72] of England's Total population have now been infected or vaccinated.
Wall of immunity:
13% Infected
44% Vaccinated 1+
13% Both
Usual caveats: time lag after vax, not 100% protective, assumes random vaxxing probability of previously infected etc.
1/
Estimated numbers of people:
7.0m Infected only
24.7m Vaccinated only
7.5m Infected & vaccinated
17.1m unexposed and susceptible
2/
The remaining 17.1m unexposed/susceptible population is heavily skewed to younger age groups.
2/3 under 25 1/3 in school age kids 5-14yo
Outbreaks and cases will expectedly be concentrated in these groups now and increasingly <18 after current vax roll out plan completed.
3/
For the 70% people after vax1/2 doses, vax+infxn and previous infxn current weighted population average protection from symptomatic infection is 80-85%.
Protection for severe illness/hospitalization/death higher.
4/
The end is in sight!
But as JVT would say it's the 88th minute and we're 3-2 up things can change.
Variants with increased transmissibility or altered effectiveness of vaccines can cause issues depending on degree. @JamesWard73 has excellent analysis.
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...
From contact tracing of 4.1k households where index vaxxed >21days and contact positive 2-14 days of index
4 Jan 4 - 28 Feb from 365k households w/ single index case and 1m+ contacts
1/
No statistical difference between Ox/AZ and Pfizer efficacy for onward transmission
No statistical difference in effect by age
Well controlled:
adjusted for age of index case and contact, sex, region, calendar week, index of multiple deprivation quintile, household type
2/
limitations:
Pillar 2 symptomatic case only so may miss asymptomatic cases (=overestimate efficacy).
Assumed contact symptom >2days of index was transmission but cd be co-primary (=underestimate),
and all 2-14 days are household transmission not independent (=underestimate)
3/