AstraZeneca/Oxford COVID-19 Vaccine

An interim analysis of 4 randomized double-blind trials of an adenovirus-vectored COVID-19 vaccine was published recently.1 Developed through a partnership between AstraZeneca and Oxford University, this vaccine is relatively inexpensive and can be stored in standard refrigerators. It has been approved for use in the UK and several other countries, but not to date in the US.

The clinical trials, which took place in Brazil, South Africa, and the UK, were designed to give 2 standard doses of the vaccine to seronegative subjects. By mistake, however, a subset of participants in the UK received only half the standard dose in the first injection. The efficacy of the vaccine in preventing symptomatic COVID-19 was 62.1% with the 2 standard doses (27 of 4440 vs 71 of 4455) and 90.0% with the low dose followed by a standard dose (3 of 1367 vs 30 of 1374); the pooled efficacy was 70.4%. Altogether, 10 patients were hospitalized, of whom 2 had severe disease, and 1 died, all in the control arm.

The reaction to the AstraZeneca interim results has understandably been focused on the surprisingly superior results with the lower-dose first injection and the relatively low efficacy rate with the standard doses, especially when compared to the ~95% efficacy in preventing symptomatic infection reported with both of the messenger RNA vaccines that are now available in the US.2,3 But all three of these vaccines have been highly effective in preventing severe disease; in all of the trials, only one case of severe disease occurred in a vaccinated subject (after the first dose in the Pfizer trial).

AstraZeneca has launched a phase 3 trial in the US (using 2 full-strength doses) designed to include 30,000 subjects. If that produces satisfactory proof of efficacy and no new surprises, emergency use authorization may be forthcoming from the FDA by late spring.

  1. M Voysey et al. Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK. Lancet 2021; 397:99.
  2. FDA authorizes Pfizer-BioNTech COVID-19 vaccine. Med Lett Drugs Ther 2021; 63:1.
  3. FDA authorizes Moderna COVID-19 vaccine. Med Lett Drugs Ther 2021; 63:9.

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