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https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00432-3/fulltext | |
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February 19, 2021 | |
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Vaccine efficacy | |
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The pooled analysis of ChAdOx1 nCoV-19 trials and exploratory analyses of the impact on immunogenicity and efficacy of extending the interval between priming and booster doses Furthermore, demonstrate the immunogenicity and protection afforded by the first dose prior to the administration of a booster dose. | |
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Across the four studies, 24 422 people were recruited and vaccinated, with 17 178 of them included in the primary analysis (8597 receiving ChAdOx1 nCoV-19 and 8581 receiving control vaccine).
COV001 (UK) recruited healthy adults aged 18–55. COV002 (UK) and COV003 (Brazil) enrolled adults aged 18 and up, with a focus on health-care workers and others at high risk of SARS-CoV-2 infection. COV005 (South Africa) enrolled adults between the ages of 18 and 65. All participants who were SARS-CoV-2 N protein seronegative at baseline had at least 14 days of follow-up after the second dose and had no evidence of previous SARS-CoV-2 infection from NAAT swabs were included in the primary analysis. All participants who received at least one dose were evaluated for safety. |
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Exploratory analyses revealed that vaccine efficacy after a single standard dose of vaccine was 76.0 % from day 22 to day 90 after vaccination.
After the second dose, efficacy was higher in participants with a longer prime-boost interval (vaccine efficacy 81.3 % [95 % CI 60.3–91.2] at 12 weeks) than in those with a short interval (vaccine efficacy 55.1 %[33.0–69.9] at <6 weeks). These findings are supported by immunogenicity data, which show that binding antibody responses are more than two-fold higher after a 12-week interval compared to a 6-week interval in people aged 18–55. |
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The ChAdOx1 nCoV-19 (AZD1222) vaccine was approved for emergency use in the UK based on interim efficacy results from 131 cases of primary symptomatic COVID-19, with efficacy based on two of the vaccine’s four trials. In the UK the vaccine will be administered in two doses, 12 weeks apart.
After another month of data collection, this report provides updated primary efficacy results. Efficacy estimates now include data from all four vaccine studies from three countries, whereas the interim analysis only included data from two studies in efficacy assessments due to the small number of cases in the smaller studies. The primary analysis backs up the interim analysis’s findings that the vaccine is effective and safe. Exploratory analyses show that a longer prime-boost interval results in higher vaccine efficacy and that a single dose of vaccine is effective in the first 90 days, providing additional evidence for current policy. |