Vaccine candidates report phase 3 studies after early safety and immune responses in phase 1/2 studies

Simon Collins, HIV i-Base

As this issue of HTB was being compiled, three research groups released data that will launch large phase 3 studies.

The first of these involved the Moderna mRNA-1273 vaccine, with phase 1 interim results published in the NEJM and first patients expected to enrol 30,000 participants in the US in a phase 3 study from 27 July 2020. [1, 2, 3]

The Lancet also published the first results on two other vaccine studies using an adenoviral vector. These studies reported good safety (fever, fatigue, and injection site pain) but no serious events. Both vaccines also generated both humoral responses to the spike glycoprotein receptor and cellular T-cell responses.

The phase 1/2 trial of the chimpanzee adenovirus-vectored vaccine (ChAdOx1 nCoV-19) being developed by the Jenner Institute at Oxford University and AstraZeneca (Oxford COVID Vaccine Trial Group) included 1077 volunteers. Neutralising antibodies were generated in more than 90% of participants that lasted out to 56 days. [4]

The phase 2 vaccine study developed by researchers in Wuhan, China with support from CanSino Biologics involved 508 participants. Seroconversion occurred in more than 96% of participants, and neutralising antibodies were generated in about 85%. More than 90% generated T-cell responses. [5]

The Lancet included a useful editorial commentary discussing short-term expectations for upcoming phase 3 research. [6]

A useful article in JAMA also summaries different approaches for five leading COVID-19 candiates. [7]

The phase 3 Oxford Vaccine Group study is already enrolling in the UK. [8, 9]

There is a useful 30-minute summary of the early results of these three candidates is given by Professor Sharon Lewin for Clinical Care Options. [10]


  1. NIH press statement. Experimental COVID-19 vaccine safe, generates immune response. (14 July 2020).
  2. Moderna press release. Moderna announces publication in the New England Journal of Medicine of interim results from phase 1 study of Its mRNA vaccine against COVID-19 (mRNA-1273). (14 July 2020).
  3. A Study to Evaluate Efficacy, Safety, and Immunogenicity of mRNA-1273 Vaccine in Adults Aged 18 Years and Older to Prevent COVID-19.
  4. Folegatti PM et al. 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. The Lancet, DOI:10.1016/ S0140-6736(20)31604-4. (20 July 2020). (article)
  5. Zhu F-C et al. Immunogenicity and safety of a recombinant adenovirus type-5-vectored COVID-19 vaccine in healthy adults aged 18 years or older: a randomised, double-blind, placebo- controlled, phase 2 trial. The Lancet. DOI:10.1016/ S0140-6736(20)31605-6. (20 July 2020). (article)
  6. Bar-Zeev N et al. Encouraging results from phase 1/2 COVID-19 vaccine trials. The Lancet. Online comment. (20 July 2020).
  7. O’Callaghan KP et al. Developing a SARS-CoV-2 vaccine at warp speed JAMA. doi:10.1001/jama.2020.12190. (6 July 2020).
  8. COVID-19 Phase II/III Vaccine Study (COV002) website.
  9. A Phase 2/3 Study to Determine the Efficacy, Safety and Immunogenicity of the Candidate Coronavirus Disease (COVID-19) Vaccine ChAdOx1 nCoV-19.
  10. Lewin S. Current Status of SARS-CoV-2 Vaccine Development. Clinical Care Options. COVID-19 resource centre. (31 July 2020).

Links to other websites are current at date of posting but not maintained.