Thread by @angryhacademic

Latest #SIRENStudy paper:
Effectiveness of BNT162b2 mRNA vaccine third doses and previous infection in protecting against SARS-CoV-2 infections during the Delta and Omicron variant waves; the UK SIREN cohort study September 2021 to February 2022
medrxiv.org/content/10.110…

During Delta period:
278 primary infections (4/10,000 person-days follow-up)
85 reinfections (0.8/10,000)

During Omicron period:
2,467 primary infections (43/10,000)
881 reinfections (33/10,000)

Relative vaccine effectiveness 0-2 months post-3rd (Pfizer) vaccine in SARS2 naïve cohort during Delta: 63 (95 % CI 40, 77) %

During Omicron:
35 (95 % CI 21, 47) %

Protection from 3rd dose waned rapidly against Omicron—no difference between 2 & 3 doses (Pfizer) after 4 months

Prior infections provided ↑ protection against omicron (67, 95 % CI 56-75 %) 3-6 months post-infection, waning to 25 % after 9 months (~3 x lower than against Delta)

⌛️3rd dose Pfizer offered short-term protection against Omicron

📉Protection from previous infections markedly diminished against Omicron

"findings demonstrate the complexity of an evolving pandemic with potential emergence of immune-escape variants"

These findings are obviously out of date now, but this 'vax n relax' strategy clearly is not a good idea @scotgov @NHSScotland