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- The ChAdOx1 nCoV-19 vaccine was found to be well-tolerated in Phase 2 of a study involving older people
- Antibody responses and T cell responses were similar in adults of different age groups
- Further work is, however, needed to see if the vaccine protects against Covid-19 disease
Early-stage results published in The Lancet this week show that the Oxford AstraZeneca vaccine, ChAdOx1 nCoV-19, is safe and provokes an immune response in healthy older adults (aged 56 years and over).
The results are similar to those seen in the vaccine candidate’s trials that included adults aged 18–55 years. It is also currently being trialled in South Africa.
Co-author, Professor Sarah Gilbert (University of Oxford) stressed the importance of knowing how the Covid vaccine behaves in people over the age of 55, during a UK Science Media Centre briefing on Thursday.
“We’re really delighted with the results. In this study, we have been trying to examine the immune responses of older adults and address the question of whether, as you get older, the immune system is less able to respond to the coronavirus vaccine that’s being developed here at Oxford," said chief investigator of the study, Professor Andrew Pollard (University of Oxford).
“And the first data are really encouraging. We are getting very good immune responses, even in the over 70s, which look very similar to those in younger adults.
“As you start rolling vaccines into older age groups, it really is critical that those common side effects, such as feeling a little bit woozy after you’ve had the first dose, are very much less in the over 50s, and even lower in the over 70s,” Pollard said.
Phase 3 trials of the COV002 study are ongoing to confirm these results, as well as establishing how effective the vaccine is in protecting against Covid-19 disease in a broader group of people, including older adults with underlying health conditions.
Results explained
In the phase 2 trial of this study, 560 participants from Oxford and Southampton were divided into three different age groups: 18–55, 56–69, and 70 and older.
Study recruitment took place during a national lockdown in the UK when vulnerable individuals were advised to self-isolate. The study, therefore, includes only healthy participants and not those with comorbidities.
Within each of these groups, participants were randomised to receive either the Oxford vaccine, or a control vaccine (the meningococcal conjugate vaccine) which wouldn’t provide protection against SARS-CoV-2.
Divided even further, participants were randomised to receive one dose of vaccine, while some received two doses.
Participants were asked to record in a diary every day any symptoms they had, either at the site of injection, or symptoms that were experienced systemically, such as headache, fever, or muscle ache.
Co-author Dr Maheshi Ramasamy (University of Oxford) explained that systemic symptoms were reported to be less troublesome in the older age groups.
The symptoms were also similar to those seen in a flu vaccine, including tiredness and headache.
“One of the most exciting things from our study was that the vaccine stimulated really good antibody production. In those individuals who received two doses of the vaccine, they had very similar antibody responses regardless of age by 28 days after that second dose,” said Ramasamy.
“It was also quite clear that two doses of vaccine are better than one dose.”
Vaccine boosts
Gilbert added that they're looking at giving people two vaccine doses and then monitoring how well those responses are maintained.
"What this could mean is that in the future when we're looking to boost people's responses, we might need to do it more often in older people than we do with younger people, but we're not thinking that we're going to need to boost people more than once a year as we do with the flu vaccine.
"We still need to collect all the data on that though," she said.
Neutralising antibody
The team also studied neutralising antibody in the participants, and found that similar levels of neutralising antibody responses were seen after two doses, regardless of age. These antibodies that block the virus from entering cells can be measure in the lab, Ramasamy explained.
“We think that this particular sort of antibody is important in protection from infection, and certainly in animal models, we’ve seen that neutralising antibody is associated with protection from lung infection.
Vaccine also stimulates T cell response
“Up until now, we’ve looked at antibody, which protects the circulating fluid (blood and tissue flow) from the virus. What we’re looking at now are T cells, which are important in identifying and killing cells that are already infected with virus,” Ramasamy said.
In the study, all age groups were found to have good T cell responses by day 14 of vaccination.
Larger studies are now underway to evaluate immunogenicity, safety and efficacy in older adults with a wider range of comorbidities.
Limitations of the study
Some of the limitations of this study include the fact that all participants were white and non-smokers, and may not be representative of the general population, the authors noted. However, participants from a range of backgrounds, countries and ethnicities are being included in the phase 3 trial of the vaccine.
"The robust antibody and T-cell responses seen in older people in our study are encouraging. The populations at greatest risk of serious Covid-19 disease include people with existing health conditions and older adults.
“We hope that this means our vaccine will help to protect some of the most vulnerable people in society, but further research will be needed before we can be sure," Ramasamy said.
