This website is intended for healthcare professionals only.
Take a look at a selection of our recent media coverage:
14th December 2020
AZD1222 is a viral vector based on an adenovirus derived from chimpanzees and subsequently modified so that it would induce a strong immune response against COVID-19. An interim analysis of the data has now been published by the Oxford Vaccine Group, based on four ongoing, and randomised controlled trials done across three countries. The trials include a Phase I/II (COV001) and Phase II/III (COV002), both from the UK, together with a Phase III trial (COV003) conducted in Brazil and a Phase I/II study (COV005) in South Africa, although three of these trials are single blind and only the South African study is double-blind. The interim data comes from all patients in the trials who received two doses of AZD1222. In COV001 patients are aged between 18 and 55 and randomised 1:1 to the test vaccine or a control vaccine (meningococcal group A, C W and Y). In COV002, participants (also aged 18 to 55) have received two doses of the vaccine, with the first being a lower dose which was boosted by the second, standard dose. However, subsequent enrolment to this arm occurred with patients aged 56 – 69 years of age and at a later stage patients aged 70 years and over and this later cohort received two standard doses of the vaccine.
The authors also reported that while COV002 was originally designed as a single dose study, this was amended to include a second booster dose. COV003 recruited individuals at high risk e.g., healthcare workers, 18 years and older and received a different dose again of the test vaccine administered up to 12 weeks apart. Finally, COV005 included healthy adults (18 – 65 years of age) who received the same two doses received in COV003. For the interim analysis, all studies were required to have at least 5 cases eligible for inclusion but neither COV001 or COV005 met these criteria and hence the interim analysis was based on only two studies. Vaccine efficacy was calculated 1 – adjusted relative risk and the primary outcome was set as virologically confirmed COVID-19 (via a swab test) combined with at least one qualifying symptom (e.g. fever, cough, shortness of breath or anosmia or ageusia.
A total of 23,848 patients were recruited across the 4 trials and 11,636 were included in the interim analysis. The majority of patients (86%) were aged between 18 and 55 and 12.2% were older than 56 years (those recruited later in the trial). In the trial with an initial lower dose, there were 33 cases of COVID-19, 3 (0.2%) in the test vaccine group and 30 (2.2%) in the control arm, which gave a vaccine efficacy of 90%. among those who received two standard doses, vaccine efficacy was 62.1%.
The authors were unable to explain why a lower followed by a standard dose resulted in higher vaccine efficacy and this is the subject of further work.
Voysey M 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 2020 doi.org/10.1016/ S0140-6736(20)32661-1