Interim results from the phase 1/2 COV001 trial evaluating the vaccine candidate ChAdOx1 nCoV-19 (AZD1222) showed that vaccination led to strong immune responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in all evaluated participants.
The ChAdOx1 nCoV-19 vaccine utilizes a replication-deficient chimpanzee adenovirus to deliver a SARS-CoV-2 protein to induce a protective immune response. The ongoing trial, led by the University of Oxford in partnership with AstraZeneca, is investigating the safety, reactogenicity and immunogenicity of ChAdOx1 nCoV-19, using a meningococcal conjugate vaccine (MenACWY) as a control, in 1077 healthy adults aged 18 to 55 years. Participants were randomized 1:1 to receive either a single dose of ChAdOx1 nCoV-19 or MenACWY as a single intramuscular injection. Ten individuals received the investigational vaccine as a 2-dose series, given 1 month apart.
According to early data recently published in The Lancet, 95% of participants treated with a single dose of ChAdOx1 nCoV-19 demonstrated a 4-fold increase in antibodies to SARS-CoV-2 one month after vaccination. Moreover, ChAdOx1 nCoV-19 induced a T-cell response in all participants that peaked by day 14 and was maintained 2 months after vaccination. “There are accumulating data to suggest T-cell responses play an important role in [coronavirus disease 2019 (COVID-19)] mitigation; individuals who were exposed but asymptomatic developed a robust memory T-cell response without symptomatic disease in the absence of a measurable humoral response,” the study authors noted.
Findings also showed that ChAdOx1 nCoV-19 elicited neutralizing antibody responses against SARS-CoV-2 in 91% (n=32/35) of study participants 1 month after vaccination and in 100% of participants after receiving a second dose. Moreover, similar levels of neutralizing antibodies were observed after 1 or 2 doses of ChAdOx1 nCoV-19 when compared with those seen in convalescent plasma samples of patients infected with COVID-19. The study authors reported a strong correlation between neutralizing antibody responses and antibody levels measured by ELISA (P <.001).
With regard to safety, transient local and systemic reactions were common with ChAdOx1 nCoV-19; these included temporary injection site pain and tenderness, pain, feverishness, chills, muscle ache, headache, and malaise. These reactions were reduced with the use of prophylactic acetaminophen and occurred less frequently after a second dose.
Professor Andrew Pollard, Chief investigator of the Oxford Vaccine Trial at Oxford University and co-author of the trial, said: “The interim phase 1/2 data for our coronavirus vaccine shows that the vaccine did not lead to any unexpected reactions and had a similar safety profile to previous vaccines of this type. The immune responses observed following vaccination are in line with what we expect will be associated with protection against the SARS-CoV-2 virus, although we must continue with our rigorous clinical trial program to confirm this. We saw the strongest immune response in participants who received 2 doses of the vaccine, indicating that this might be a good strategy for vaccination.”
Phase 2/3 trials are currently underway in the UK, Brazil and South Africa, and are expected to begin soon in the US; the trials are recruiting a diverse population of participants, including older individuals with comorbidities, healthcare workers, and others at high risk of exposure. The researchers noted that the vaccine will also be evaluated in children once enough safety data has been collected in adult studies.
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