Abstract
Single-dose administration and the influence of the timing of the booster dose on immunogenicity and efficacy of ChAdOx1 nCoV-19 (AZD1222) vaccine: a pooled analysis of four randomised trials
Highlights
We report a prespecified full primary analysis of the efficacy of the ChAdOx1 nCoV-19 vaccine more than 14 days after a second dose, with 332 symptomatic cases of COVID-19 in an analysis population of 17 178 study participants and an efficacy of 66·7%, confirming the results of our published interim analysis[4] (131 cases reported in the interim analysis)
The analysis presented here provides strong evidence for the efficacy of two standard doses of the vaccine, which is the regimen approved by the Medicines and Healthcare products Regulatory Agency (MHRA) and other regulators
Two criteria that contribute to decision making in this area are the effect of prime-boost interval on protection after the second dose and the degree to which the vaccinated individual is at risk of infection during the time period before the booster dose, if there were either reduced efficacy with a single dose or rapid waning of efficacy before the second vaccination
Summary
Vaccine supply is likely to be scarce, at least initially, and so policy makers must decide how best to deliver available doses to achieve greatest public health benefit, and different approaches have been taken in different settings. In the UK, second doses of both available vaccines (a viral vector and mRNA vaccine) are being delivered with an interval of up to 12 weeks,[5,6] and this regimen is being considered by several other countries.[7,8] By contrast, WHO has recently recom mended a maximum 6 week interval between the two doses of the same mRNA vaccine.[9]. The safety and immunogenicity of the vaccine were assessed in four randomised controlled trials in the UK, Brazil, and South Africa, and results in cohorts of healthy adults and in adults aged 70 years or Research in context
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