The Ad5-vectored COVID-19 vaccine tested on people above 55 years of age, is considered a step up from another vaccine being developed by the UK
A vaccine developed in China for the novel coronavirus (SARS-CoV-2) that causes COVID-19 has entered the third phase of clinical trials, according to a researcher quoted in a release by The Lancet journal July 20, 2020.
The Adenovirus type-5-vectored (Ad5-vectored) COVID-19 vaccine induced an immune response during the second phase of the trial, said the release, citing a study by The Lancet.
The trial is conducted to evaluate the safety and immunogenicity of the Ad5-vectored COVID-19 vaccine developed by the Beijing Institute of Biotechnology and CanSino Biologics Inc.
“Phase 3 trials are now underway,” said Feng-Cai Zhu, a professor at the Jiangsu Provincial Center for Disease Control and Prevention, China, who also leads the research into the vaccine.
“This is an important step in evaluating this early-stage experimental vaccine,” he added.
Another vaccine — ChAdOx1 nCoV-19 being developed by researchers at the University of Oxford in the United Kingdom — is currently on its second phase.
A step up from UK vaccine
The Ad5-vectored vaccine is, however, said to be a step up because 13 per cent of the people who participated in the trial were 55 years and older. The vaccine was tested on 508 people, compared to 195 participants from the first phase.
Approximately 61 per cent of the participants in the second phase were between 18 and 44 years, while 26 per cent were between 45 and 54 years.
The ChAdOx1 nCoV-19 vaccine, on the other hand, is yet to be tested on older people. The Lancet, however, said ChAdOx1 nCoV-19 is eligible to be evaluated in a phase 3 trial.
The second phase of a vaccine trial is a necessary and crucial step to turn an early-stage experimental vaccine into a promising candidate.
The results from the second phase of the Ad5-vectored vaccine will be evaluated for the third phase as well.
Vaccine uses weakened human common cold virus
The vaccine uses a weakened human common cold virus known as the adenovirus, which infects human cells readily but is incapable of causing disease.
This helps deliver genetic material that codes the SARS-CoV-2 spike protein into the cells. These cells, in turn, produce the spike protein and travel to the lymph nodes, where the immune system creates antibodies that recognise the spike protein and fight off the virus.
A few limitations
The vaccine trial, however, has a few limitations, according to The Lancet study. Pre-existing immunity to the human adenovirus and older age is likely to partially hamper specific immune responses to vaccination, particularly for antibody responses.
Older participants generally had significantly lower immune responses, compared to their younger counterparts, the study said.
Elderly individuals faced a high risk of serious illness and even death associated with COVID-19, becoming an important target population for a COVID-19 vaccine, said Wei Chen, a professor at the Beijing Institute of Biotechnology.
“It is possible that an additional dose may be needed to induce a stronger immune response in the elderly population,” he said, adding further research was underway to evaluate this.
Geographical limitations
The baseline immunity found in the trial was representative of Chinese adults as it was conducted in Wuhan, the study pointed out.
Other countries may have different rates of immunity that must be considered, the study said.
Although COVID-19 appears to have a more benign course in children with almost no fatalities reported, an ideal vaccine candidate for the pandemic should cover susceptible populations in all ages. This trial, however, did not include children.
It followed participants for 28 days and no data about the durability of the vaccine-induced immunity is available from this study.
No participants were, however, exposed to SARS-CoV-2 after vaccination.
It was, thus, not possible to determine the efficacy of the vaccine candidate or any immunological risk associated with antibodies induced by vaccination when being exposed to the virus, warned the study.
The third phase trials, thus, need to confirm whether the vaccine candidate effectively protects against the SARS-CoV-2 infection.
Future studies will be needed to assess the feasibility of using the Ad5-vectored COVID-19 vaccine to provide protection for high-risk populations or for outbreak intervention.
Evidence from the second phase, nevertheless indicates the Ad5-vectored COVID-19 vaccine has a good safety profile, with only mild, transient adverse effects related to vaccination.
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