The coronavirus vaccine developed by teams at the University of Oxford has been shown to trigger a robust immune response in healthy adults aged 56-69 and those over 70 years of age.
The findings published in ‘Lancet’ on Thursday based on 560 healthy adult volunteers shows that the ChAdOx1 nCoV-19 vaccine is “safe and well-tolerated” with a lower reactogenicity profile in older adults than in younger adults, meaning the older age groups could build immunity to the disease.
“These findings are encouraging because older individuals are at disproportionate risk of severe Covid-19 and so any vaccine adopted for use against SARS-CoV-2 [COVID-19] must be effective in older adults,” the researchers note.
The team is also testing whether the vaccine stops people developing Covid-19 in larger Phase 3 trials and early results from this crucial stage are expected in the coming weeks.
"We were pleased to see that our vaccine was not only well-tolerated in older adults, but also stimulated similar immune responses to those seen in younger volunteers,” said Dr Maheshi Ramasamy, an investigator at the Oxford Vaccine Group.
"The next step will be to see if this translates into protection from the disease itself," she said.
This means there are now four promising vaccines on the horizon after Pfizer-BioNTech, Sputnik and Moderna already reporting good preliminary data from Phase 3 trials.
The UK has already ordered 100 million doses of the Oxford vaccine, being manufactured by pharma major AstraZeneca. The vaccine also has a tie-up with the Serum Institute of India.
Professor Andrew Pollard, the head of Oxford's vaccine trial team, said he is "absolutely delighted" with the latest results.
Crucially, the study also found no “suspected unexpected serious adverse reactions” during this stage of the trial. The 560 healthy adult volunteers who took part in the phase two trials were given two doses of the vaccine candidate or a placebo.
"Inducing robust immune responses in older adults has been a long-standing challenge in human vaccine research,” said Dr Angela Minassian, an investigator at the University of Oxford and honorary consultant in infectious diseases.
"To show this vaccine technology is able to induce these responses, in the age group most at risk from severe Covid-19 disease, offers hope that vaccine efficacy will be similar in younger and older adults," she said.
Thursday’s report on data from the Phase 2 trial of the ChAdOx1 nCoV-19 vaccine shows that volunteers in the trial demonstrate similar neutralising antibody titres, and T cell responses across all three age groups – 18-55, 56-79, and 70+.
“The outcomes reported at this stage of the study include the safety of the vaccine and the immune responses of participants in different age groups following vaccination. It is important to assess how well the vaccine works in older people, as these age groups are more severely affected by Covid-19 disease,” the study notes.
“Sometimes vaccines are less effective in older people, so it is important to find out at an early stage how well the immune system responds to the vaccine in those over the age of 55,” it adds.
Antibodies play an important role in the immune response to viruses. The latest trial assessed both the quantity and quality of antibody found in participant blood samples.
An ELISA (enzyme-linked immunosorbent assay – a plate-based laboratory technique) was used to detect and measure the number of antibodies in the blood that recognise the spike protein.
In addition to measuring the quantity of antibody, the study also examined the quality of antibody, its ability to neutralise the virus. Like the previous study, good levels of neutralising antibodies were produced, and this was consistent across all age groups, the research team notes.
T cells play an important role in the immune response to viral infections. Some T cells are responsible for killing viruses inside infected cells, whilst others are responsible for providing help to other components of the immune response.
There is increasing evidence that T cells play an important role in preventing serious disease with natural infection of the Covid-19 virus.
The latest trial shows that after a single vaccination, T cell responses were highly comparable in all ages and across different doses.
“The participants in this study continue to be monitored to assess how well the immune responses are maintained over a longer time period,” the research team said.
“To assess whether the vaccine works to protect from Covid-19, the statisticians in our team will compare the number of infections in the control group with the number of infections in the vaccinated group. How quickly we reach the numbers required will depend on the levels of virus transmission in the community. With the current low transmission levels in the UK, this could take many months,” they add.
The researchers say they have completed recruitment of over 10,000 people to its Phase 2-3 study, which aims to assess the efficacy of the vaccine and to compare the different dose schedules.
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