Alliance for Pandemic Preparedness

April 22, 2021

Safety and Efficacy of Single-Dose Ad26.COV2.S Vaccine against Covid-19



Keywords (Tags):

  • The SARS-CoV-2 single-dose adenovirus vector vaccine Ad26.COV2.S (Johnson & Johnson) protected against moderate to severe-critical COVID-19 ≥14 days after administration with 66.9% efficacy (95% CI: 59-73.4%) in a randomized, double-blind placebo-controlled phase 3 trial. 116 cases occurred among those receiving the vaccine (n=19,691) vs 348 cases in the placebo group (n=19,691). Efficacy ≥28 days after administration was 66.1% (66 vs 193 cases; 95% CI: 55-74.8%). Vaccine efficacy against severe-critical COVID-19 was 76.7% at onset ≥14 days and 85.4% at onset ≥28 days.
  • Among participants in South Africa where 94.5% (86 of 91) of cases had the B.1351 variant, vaccine efficacy was 52% at onset ≥14 days and 64% at onset ≥28 days against moderate to severe-critical COVID-19. Efficacy against severe-critical COVID-19 was 73.1% at onset ≥14 days and 81.7% at onset ≥28 days.
  • While serious adverse events were balanced across the vaccine and placebo groups, imbalance towards the vaccine group were observed for thromboembolic events (11 vs. 3 cases), seizure (4 vs 1 cases), and tinnitus (6 vs 0 cases). The authors could not determine a causal relationship with the vaccine.

Sadoff et al. (Apr 21, 2021). Safety and Efficacy of Single-Dose Ad26.COV2.S Vaccine against Covid-19. New England Journal of Medicine.