By Ruchi Jhonsa, Ph.D.
The experimental coronavirus vaccine developed by the University of Oxford, together with pharmaceutical giant AstraZeneca was able to generate strong T cell and antibody immune response in Phase 1 clinical trials.
The ChAdOx1 nCoV-19 vaccine was found to be well-tolerated, without any adverse effects. Common side effects included fatigue, headache, pain at the site of injection, fever, muscle aches, and chills. The highly anticipated results were published in the medical journal The Lancet on Monday.
With a single dose of vaccine, spike-protein specific T-cell response peaked on Day 14 while the cells remained in circulation even two months later. However, a spike in the cellular response was not observed following a booster dose. Antibody response, on the other hand, rose by day 28 and remained elevated to day 56 following a booster dose.
When one tries to determine the efficacy of the vaccine, they generally look for levels of what is called “Neutralizing antibodies.” These antibodies hold power to kill the virus in the vicinity while blocking their interaction with human cells. Thus, they provide the best evidence that protective immunity has been established. However, the study showed a discrepancy in the number of participants who produced neutralizing antibody responses on two different tests. While one showed 100%, the other showed a 91% response. Although this is a good reaction to the vaccine, whether this will create a long-lasting immunity against the virus is still a question.
The vaccine is made up of a weakened version of a chimpanzee-infecting common cold virus that carries a piece of the genetic material of the SARS-CoV-2 spike protein. Following vaccination, the spike protein is produced, which would induce the immune system to generate antibodies and T cells against the novel coronavirus.
While this trial was done in the 18-55 age group, much younger than the group who would need it the most, the trials are underway at various sites in the UK and overseas in participants who are older with comorbidities and are at higher risk for SARS-CoV-2 exposure. Concurrently, later-stage trials are ongoing in the UK, Brazil, and South Africa and are due to start in the US that will determine vaccine efficacy in a diverse population.
According to the authors, “These results, together with the induction of both humoral and cellular responses, support large scale evaluation of this candidate vaccine in an ongoing phase-3 program.”
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