Safety and Immunogenicity of ChAdOx1 nCoV-19 Vaccine

Jul 23, 2020
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Authors:
Folegatti PM, Ewer KJ, Aley PK, et al., on behalf of the Oxford COVID Vaccine Trial Group.
Citation:
Safety and Immunogenicity of the ChAdOx1 nCoV-19 Vaccine Against SARS-CoV-2: A Preliminary Report of a Phase 1/2, Single-Blind, Randomised Controlled Trial. Lancet 2020;Jul 20:[Epub ahead of print].
Summary By:
Salim Hayek, MD, FACC

Quick Takes

  • A chimpanzee adenovirus-vectored vaccine (ChAdOx1 nCoV-19) expressing the SARS-CoV-2 spike protein had a higher incidence of mild to moderate adverse effects compared to the meningococcal vaccine.
  • A single dose of the vaccine led to persistent antibody and cellular immune responses.
  • Preliminary findings of efficacy in preventing SARS-CoV-2 infection are pending.

Study Questions:

Is a chimpanzee adenovirus-vectored vaccine (ChAdOx1 nCoV-19) expressing the SARS-CoV-2 spike protein safe and immunogenic?

Methods:

The authors conducted a phase 1/2, single-blind, randomized controlled trial at five sites in the United Kingdom through which 1,077 healthy adults enrolled between April 23 and May 21 were randomly assigned 1:1 to receive ChAdOx1 nCoV-19 at a dose of 5 × 10¹⁰ viral particles or a meningococcal conjugate vaccine (MenACWY). Ten patients were enrolled in a ChAdOx1 nCoV-19 prime boost group, in which they received a second dose of the vaccine at 28 days. The co-primary outcomes were to assess efficacy, as measured by cases of symptomatic virologically confirmed coronavirus disease 2019 (COVID-19), and safety, as measured by the occurrence of serious adverse events. Antibody and cellular responses were assessed in a subset of patients at baseline and following vaccination by measuring total IgG against SARS-CoV-2 spike protein, various neutralization assays, and interferon-gamma levels. This manuscript only reports preliminary data on safety and immunogenicity.

Results:

Overall, half of the participants were women, 90% were white, and the median age of participants was 35 years (interquartile range, 28-44). Participants who received the ChAdOx1 nCoV-19 vaccine were more likely to experience mild to moderate pain, fatigue, feeling feverish, chills, malaise, and headache (60-70%) compared to the those who received the MenACWY vaccine (40-50%). There were no serious adverse events related to ChAdOx1 nCoV-19 by 28 days post-vaccination. In the ChAdOx1 nCoV-19 group, antibodies against SARS-CoV-2 spike protein peaked by day 28 and remained elevated to day 56. The majority of patients (>90%) achieved antibody titers for 80% viral neutralization after a single dose. Interferon-gamma levels peaked at day 14 and declined at day 56.

Conclusions:

A single dose of ChAdOx1 nCoV-19 vaccine had a higher incidence of mild to moderate adverse effects compared to MenACWY and induced anti–SARS-CoV-2 immune responses without severe adverse effects.

Perspective:

This study dovetails recent reports of phase 1 trials showing various vaccine formulations for SARS-CoV-2 being safe and immunogenic; inducing both antibody and T-cell responses. This trial is notable for including the meningococcal vaccine as a comparator. While self-limited reactions were more common, the ChAdOx1 nCoV-19 was overall well tolerated. What is exciting about this specific trial is that it aims to assess the efficacy of the vaccine and has enrolled patients accordingly. We now await with great anticipation the preliminary findings on efficacy while phase 3 trials are underway in various countries.

Clinical Topics: COVID-19 Hub, Prevention

Keywords: Antibodies, Chills, Coronavirus, COVID-19, Fatigue, Fever, Headache, Meningococcal Vaccines, Primary Prevention, SARS Virus, severe acute respiratory syndrome coronavirus 2


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