Authors: Katherine Gordon, Future Science Group
It is widely accepted that the only long-term solution to the COVID-19 pandemic is to develop and globally distribute an effective vaccine against the virus. There are currently over 100 candidate vaccines in development but, as of now, only one of these candidates has reached the Phase I clinical testing stage.
The clinical trial tested a new adenovirus type 5 vectored COVID-19 (Ad5-nCoV) vaccine. The results, published recently in The Lancet, suggested that the vaccine is safe in humans and induces a rapid immune response, though further trials will be needed to confirm whether or not these immune responses protect against SARS-CoV-2 infection.
The new Ad5-nCoV vaccine, which uses a weakened adenovirus to deliver genetic material coding for the SARS-CoV-2 spike protein to the cells, was tested in 108 healthy adult volunteers aged 18–60 from a single site in Wuhan, China. The participants we divided into three groups and assigned to receive a low, medium or high dose of the vaccine, with blood tests at regular intervals.
At all doses, the vaccine was well tolerated and no serious adverse effects were reported in the first 28 days post immunization. Most adverse effects were mild, with 83% of those receiving low and medium doses and 75% of those receiving high doses reporting at least one mild adverse event, most commonly pain, fever, fatigue or headache, within the first 7 days, but these persisted for less than 48 hours.
Within 2 weeks, the researchers observed some form of immune response produced by the vaccine at all doses in the form of binding antibodies, and some volunteers had developed detectable neutralizing antibodies against SARS-CoV-2. Both had increased considerably by day 28.
Further, in the majority of volunteers, the vaccine stimulated a rapid T cell response, with T cell levels peaking at day 14. By day 28, almost all participants displayed either a positive T cell response or possessed detectable neutralizing antibodies against SARS-CoV-2, suggesting the vaccine can successfully induce a rapid immune response against the virus.
“These results represent an important milestone. The trial demonstrates that a single dose of the new Ad5-nCoV vaccine produces virus-specific antibodies and T cells in 14 days, making it a potential candidate for further investigation,” explained Wei Chen (Beijing Institute of Biotechnology, China), one of the authors for this study.
While the results of the trial are promising, further research is needed. “These results should be interpreted cautiously,” noted Chen. “The challenges in the development of a COVD-19 vaccine are unprecedented, and the ability to trigger these immune responses does not necessarily indicate that the vaccine will protect humans from COVID-19. This result shows a promising vision for the development of COVID-19 vaccines, but we are still a long way from this vaccine being available to all.”
A randomized, double-blinded, placebo-controlled Phase II trial of the Ad5-nCoV vaccine has already been initiated in Wuhan to determine whether these results can be replicated over a longer observation period and with a larger, more representative sample size.
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Sources: Zhu FC, Li YH, Guan XH et al. Safety, tolerability, and immunogenicity of a recombinant adenovirus type-5 vectored COVID-19 vaccine: a dose-escalation, open-label, non-randomised, first-in-human trial. Lancet doi:10.1016/S0140-6736(20)31208-3 (2020); www.eurekalert.org/pub_releases/2020-05/tl-tlf052220.php