In a new study, researchers report promising early-stage results from a phase 1/2 clinical trial of the UK’s vaccine candidate against SARS-CoV-2 (the virus that causes COVID-19).
The early-stage trial finds that the vaccine is safe, causes few side effects, and induces strong immune responses in both parts of the immune system—provoking a T cell response within 14 days of vaccination, and an antibody response with 28 days.
The research was conducted by a team at the University of Oxford and elsewhere.
An ideal vaccine against SARS-CoV-2 should be effective after one or two vaccinations, work in target populations including older adults and those with other health conditions, confer protection for a minimum of six months, and reduce onward transmission of the virus to contacts.
The new study included 1,077 healthy adults aged 18-55 years with no history of COVID-19 and took place in five UK hospitals between 23 April and 21 May 2020.
The vaccine was found to have an acceptable safety profile and there were no serious adverse events. Fatigue and headache were the most commonly reported reactions.
The authors found that there were strong antibody and T cell responses from the vaccine. T cell responses targeting the SARS-CoV-2 spike protein were markedly increased, peaking 14 days after vaccination.
Antibody responses peaked by day 28 and remained high until the measurement at day 56 in the trial for those given a single vaccine. This response was boosted by a second dose.
The team says the current trial is too preliminary to confirm whether the new vaccine meets these requirements, but phase 2 (in the UK only) and phase 3 trials to confirm whether it effectively protects against SARS-CoV-2 infection are happening in the UK, Brazil and South Africa.
The new vaccine is a chimpanzee adenovirus viral vector (ChAdOx1) vaccine that expresses the SARS-CoV-2 spike protein.
It uses a common cold virus (adenovirus) that infects chimpanzees, which has been weakened so that it can’t cause any disease in humans, and is genetically modified to code for the spike protein of the human SARS-CoV-2 virus.
This means that when the adenovirus enters vaccinated people’s cells it also delivers the spike protein genetic code.
This causes these people’s cells to produce the spike protein and helps teach the immune system to recognize the SARS-CoV-2 virus.
The immune system has two ways of finding and attacking pathogens—antibody and T cell responses.
This vaccine is intended to induce both, so it can attack the virus when it’s circulating in the body, as well as attacking infected cells.
The researchers hope this means the immune system will remember the virus so that the vaccine will protect people for an extended period.
However, they need more research before we can confirm the vaccine effectively protects against SARS-CoV-2 infection, and for how long any protection lasts.
One author of the study is Professor Andrew Pollard, University of Oxford, UK.
The study is published in The Lancet.
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