Thread by @freja_kirsebom

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:

assets.publishing.service.gov.uk/government/upl…

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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.

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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.

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Amongst those who received two doses of Pfizer (BNT162b2), VE against symptomatic disease dropped to ~50% 10 weeks after a Pfizer (BNT162b2) booster and ~70% 5-9 weeks after a Moderna (mRNA-1273) booster.

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To investigate VE against hospitalisation, symptomatic cases were first linked to the Emergency Care Dataset to identify admissions 0 to 14 days after the positive test. Cox survival analysis was then used to estimate the risk of hospital admission by vaccination status.

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The odds ratios for symptomatic disease were multiplied by the hazard ratios (HR) for hospitalisation among symptomatic cases in order to estimate VE against hospitalisation.

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For symptomatic cases, 3 doses of vaccine (any manufacturer) was associated with a 68% reduced risk of hospitalisation. When combined with VE against symptomatic disease, this was equivalent to a VE against hospitalisation of 88% 2+ weeks after a booster dose.

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We hope to soon be able to estimate VE against hospitalisation using the test-negative case control design. We did not yet have enough data to stratify VE against hospitalisation by vaccine brand, but will also be looking at this as soon as possible.

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Further data is also needed to investigate the duration of protection against severe disease with Omicron conferred by the vaccines. However, experience with previous variants suggests this will be longer than protection against symptomatic disease.

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The report also contains updates on what we know so far about Omicron severity - see below from @kallmemeg for an explainer

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https://twitter.com/kallmemeg/status/1476932349694775303