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.

Among those who received an AZ (ChAdOx1-S) primary course, VE was ~60% 2-4 weeks after either a Pfizer (BNT161b2) or Moderna (mRNA-1273) booster. VE against symptomatic disease dropped to ~35% by 10 weeks after a Pfizer booster, and ~45% 5-9 weeks after a Moderna booster.

Among those who received a Pfizer (BNT161b2) primary course, VE was ~70% 1 week after a Pfizer booster, dropping to ~45% after 10+ weeks. VE after a Moderna (mRNA-1273) booster stayed around 70-75% up to 9 weeks after the booster.

We also had enough data to look at VE against Omicron following a primary course of Moderna (mRNA-1273) for the first time. VE against symptomatic disease was lower for Omicron than Delta. At 2-4 weeks after dose 2, VE was ~50%. This dropped to 0% at 20-24 weeks post dose 2.

We trialled an analysis using a survival model to estimate VE against hospitalisation but the number of Omicron cases admitted to hospital following a positive Pillar 2 test was still too small to estimate VE.

However, based on experience with previous variants, we do expect VE against the more severe outcomes such as hospitalisation to be substantially higher than VE against symptomatic infection and we will be investigating this as soon as possible!

Vaccine effectiveness is just a small part of the Variant Tech Briefing. See below from @kallmemeg for an explainer on the whole report, including severity and re-infection analysis


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More from @freja_kirsebom

10 Dec
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.

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