Thread by @freja_kirsebom

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.

https://twitter.com/UKHSA/status/1479526192428503044

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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)).

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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.

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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.

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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%.

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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.

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https://twitter.com/UKHSA/status/1479526204080377856

Full details of our analysis can be found here:

khub.net/documents/1359…

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