Today we publish our latest analysis where we stratify by age to investigate vaccine effectiveness (VE) against Omicron in adults aged 65 years and older in England.

This week's analysis is restricted to adults aged 65+ who reported symptoms and tested in Pillar 2 (community testing) between 27th November and 31st December 2021. Cases were defined as the Omicron or Delta variant based on whole genome sequencing, genotyping, or SGTF.

As before, a test negative case control design was used to estimate VE against symptomatic COVID-19 with the Omicron variant compared to the Delta variant.

VE against symptomatic disease in older adults was lower for Omicron compared to Delta. There was minimal/no effect of the vaccines against mild disease with the Omicron variant from 20 weeks after the second dose of either a ChAdOx1-S (AZ) or BNT162b2 (PF) primary course.

Among those aged 65+ who had received 2 doses of ChAdOx1-S (AZ), at 2-4 weeks after a booster dose VE ranged from 62-65%, dropping to 48% and 56% at 5-9 weeks for the BNT162b2 (PF) and mRNA-1273 booster (MD). For the BNT162b2 booster, VE dropped further to 32% at 10+ weeks.

Among those aged 65+ who had received 2 doses of BNT162b2 (PF) followed by a BNT162b2 (PF) booster, VE was 65% at 2-4 weeks post booster, dropping to 49% at 5-9 weeks and 31% at 10+ weeks.

For those aged 65+ who had received 2 doses of BNT162b2 (PF) followed by a mRNA-1273 (MD) booster, VE was 70% at 2-4 weeks post the booster, dropping to 57% at 5-9 weeks.

Pillar 2 symptomatic cases aged 65+ were linked to the Emergency Care Dataset (ECDS) to identify hospital admissions via emergency care 0 to 14 days after the positive test. Cox survival analysis was used to estimate the risk of hospital admission by vaccination status.

To estimate VE against hospitalisation the odds ratios (OR) for symptomatic disease were multiplied by the hazard ratios (HR) for hospitalisation among symptomatic cases: VE(hospitalisation) = 1 - (OR (symptomatic disease) x HR (hospitalisation)).

At 2-9 weeks post the third dose, receiving 3 doses of a vaccine was associated with an 89% reduced risk of hospitalisation among symptomatic cases aged 65+ with the Omicron variant. This remained high at an 85% reduced risk of hospitalisation at 10+ weeks.

When combined with VE against symptomatic disease this was equivalent to VE against hospitalisation of 94% 2-9 weeks after the booster dose and 89% at 10 weeks post the booster dose in those aged 65 years or older.

Here, we find that VE against symptomatic disease wanes rapidly in those aged 65+. Protection against hospitalisation is much greater than that against symptomatic disease, in particular after a booster dose, where estimated VE against hospitalisation is around 90-95%.

These data support the latest JCVI decision on the booster programme in England, where fourth doses (second booster vaccines) are not being recommended for older adults.


Full details of our analysis can be found here:…


• • •

Missing some Tweet in this thread? You can try to force a refresh

Keep Current with Freja Kirsebom

Freja Kirsebom Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!


Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @freja_kirsebom

31 Dec 21
This week, we were able to estimate vaccine effectiveness (VE) against hospitalisation for the first time. In short, good news. VE after a booster is close to 90%. The full update from our team is published in this week's technical briefing update:…

As before, we first used a test-negative case control study design to estimate VE against symptomatic disease. This analysis included tests between 27th November and 24th December, and included 169,888 Delta cases and 204,036 Omicron cases.

Amongst those who received two doses of AZ (ChAdOx1-3), VE against symptomatic disease dropped to ~40% 10 weeks after a Pfizer (BNT162b2) booster and ~60% 5-9 weeks after a Moderna (mRNA-1273) booster.

Read 10 tweets
23 Dec 21
An update from our team on the latest vaccine effectiveness (VE) estimates against symptomatic infection with the Omicron variant has now been published in the UKHSA Variant Technical Briefing 33 (page 24).…

With more data available, we now have better estimates of VE following a booster (Pfizer or Moderna) after either an AZ or Pfizer primary course. We still did not have enough data to estimate VE against hospitalisation but we will be looking at this as as soon as possible.

As last time, we used a test-negative case control study design to estimate VE against symptomatic COVID-19 disease. This analysis included Pillar 2 testing data from 27th November to 17th December. Here, we had data from 68,489 Omicron cases and 147,597 Delta cases.

Read 9 tweets
10 Dec 21
Our first initial estimates of vaccine effectiveness (VE) against symptomatic disease with the Omicron variant are now out. In short, VE remains high following a Pfizer booster after AZ or Pfizer, but is reduced after two doses.

More below 👇

We used a test negative case control design to estimate VE against symptomatic COVID-19 with the Omicron variant compared to Delta. The odds of vaccination in PCR positive cases was compared to the odds of vaccination in those who test negative.

Pillar 2 tests were classified as either Delta or Omicron from the period 27/11 – 6/12 based on sequencing and SGFT where sequencing wasn’t available. From 27/11, at least 80% of PCR tests which included the S-gene as a target and which had SGTF were the Omicron variant.

Read 11 tweets

Did Thread Reader help you today?

Support us! We are indie developers!

This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Too expensive? Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal

Or Donate anonymously using crypto!


0xfe58350B80634f60Fa6Dc149a72b4DFbc17D341E copy


3ATGMxNzCUFzxpMCHL5sWSt4DVtS8UqXpi copy

Thank you for your support!

Follow Us on Twitter!