COVID-19 Vaccines: AstraZeneca Resumes Trial; Pfizer, BioNTech Look to Expand Study

The Medicines Health Regulatory Authority confirmed that the AZD1222 trial could proceed after a UK committee concluded its investigations.

AstraZeneca has resumed a phase 3 clinical trial investigating AZD1222, its coronavirus disease 2019 (COVID-19) vaccine candidate, after an unexplained illness led the Company to pause the trial and others across the globe.

The Medicines Health Regulatory Authority confirmed that the trial could proceed after a UK committee concluded its investigations, however, no further medical information was disclosed. In a statement, AstraZeneca said that trial investigators and participants “will be updated with the relevant information and this will be disclosed on global clinical registries.” The Company will be working with health authorities to see when the AZD1222 clinical trial program can resume in other parts of the world.

AZD1222 utilizes a replication-deficient chimpanzee viral vector (weakened adenovirus) to deliver a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) protein to induce a protective immune response. Interim results from the phase 1/2 COV001 trial showed that AZD1222 elicited strong immune responses against SARS-CoV-2 in healthy adults. With regard to safety, transient local and systemic reactions were reported to be common; these included temporary injection site pain and tenderness, pain, feverishness, chills, muscle ache, headache, and malaise.

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Additionally, Pfizer and BioNTech announced that they have submitted an amended protocol to the Food and Drug Administration (FDA) to expand the enrollment of a phase 3 trial investigating their COVID-19 vaccine candidate, BNT162b2. The Companies are looking to expand enrollment from 30,000 to 44,000 participants and also include new study populations. If approved, the trial will aim to enroll participants as young as 16 years of age, as well as those with chronic, stable HIV, hepatitis C or hepatitis B infection.

BNT162b2 is a nucleoside-modified messenger RNA (modRNA) vaccine that encodes an optimized SARS-CoV-2 full-length spike protein antigen. The investigational vaccine emerged as the strongest candidate based on available data demonstrating robust immune response and overall tolerability.

In a statement, the Companies noted that they are still on track to have efficacy data by the end of October 2020. The vaccine candidate was recently granted Fast Track designation, which allows for expedited review by the FDA. 


  1. COVID-19 vaccine AZD1222 clinical trials resumed in the UK. Accessed September 14, 2020.
  2. Pfizer and BioNTech propose expansion of pivotal COVID-19 vaccine trial. Accessed September 14, 2020.