A coronavirus vaccine candidate being developed by the University of Oxford has shown promise in the next stage of its clinical trial.
Hopes were raised in July when the jab was found to induce an immune response in hundreds of healthy volunteers.
While experts hailed the results “promising”, “encouraging” and “extremely positive”, many stressed this was just the first step of the lengthy clinical trial process before a vaccine can be approved for public use.
After testing the jab on 560 healthy adults, of whom 240 were over 70, the Oxford scientists found the vaccine brought about a similar immune response among all the participants.
The older adults were even found to tolerate the infection better than their younger counterparts.
An effective vaccine has long been hailed a route back to life as we once knew it. Early research suggests the coronavirus is mild in four out of five cases, however, the elderly are significantly more likely to develop complications.
Older people also tend to respond less effectively to any immunisation, making it particularly important for scientists to demonstrate their jab could protect this vulnerable group.
The Oxford team stressed it is unclear whether the immune response translates into protection against the coronavirus, which should be uncovered in future trials.
This new study is the fifth published trial of a coronavirus vaccine that has been tested among older people.
Preliminary data on Pfizer’s jab, which is at a more advanced clinical stage than the Oxford team’s, suggests it protects 94% of adults over 65.
Moderna’s candidate is said to be nearly 95% effective at warding off the coronavirus, however, full data on how different age groups respond to the jab are not available.
The firm’s chief medical officer Tal Zaks told the BBC the vaccine “does not appear to lose its potency” with age.
Professor Andrew Pollard, lead author of the Oxford research, said: “Immune responses from vaccines are often lessened in older adults because the immune system gradually deteriorates with age, which also leaves older adults more susceptible to infections.
“As a result, it is crucial COVID-19 [the disease caused by the coronavirus] vaccines are tested in this group, who are also a priority group for immunisation.”
After any animal or laboratory studies, a potential vaccine enters a phase 1 trial, where it is usually tested for safety in healthy volunteers.
If successful, a phase 2 trial involves testing the jab in a larger group to again determine safety, as well as the optimal dose.
As part of the Oxford vaccine’s phase 2 trial, the scientists recruited 160 volunteers aged 18 to 55, 160 aged 56 to 69 and 240 aged 70 or over.
The participants either received the Oxford team’s vaccine candidate – called ChAdOx1 – at a standard or low dose, or were given a control jab against the bacteria that can cause meningitis.
Those over 55 were either given a single dose of ChAdOx1 or two doses 28 days apart.
The participants were recruited during the UK’s first lockdown, when vulnerable individuals were advised to self-isolate.
The study therefore only included healthy participants, despite statistics repeatedly flagging people with underlying health conditions are more at risk of coronavirus complications.
Before receiving the vaccine, all the participants had a blood test to determine if they had immune-fighting proteins called antibodies against the coronavirus, which would imply they had overcome the infection naturally.
Those with antibodies were excluded, except for the 18 to 55 year olds in the standard dose double group.
Watch: Can you catch coronavirus twice?
Results reveal the vaccine induced an antibody response within 28 days of a single low or standard dose jab across all the participants.
Following a booster, antibody levels had increased by day 56, irrespective of the dose administered or the age of the participants.
Fourteen days after the booster, 208 out of 209 (more than 99%) of the participants had neutralising antibodies, which stop a virus from infecting the body by affecting how the molecules on its surface enter cells.
Antibodies are specific to each virus and lock onto their surface, neutralising or “marking” it for destruction by other immune cells.
The results also reveal the vaccine brought about a T-cell response, peaking 14 days after the first vaccination. This occurred regardless of the participant’s age, or whether they were given a low or standard dose.
There are two types of T-cells: helper and killer.
Helper T-cells stimulate antibody production and assist in the development of killer cells. Killer T-cells directly destroy body cells that have already been infected by a virus.
T-cells also send out messages that instruct the rest of the immune system to ramp up its response.
When it comes to safety, any side effects that occurred within seven days of one standard vaccine dose were less common in the older adults.
These adverse events included temporary pain, tenderness, redness and swelling at the site of the injection. Some also reported temporary fatigue, headache, feverishness, muscle aches and generally feeling unwell.
“The World Health Organization has outlined a number of critical factors for COVID-19 vaccines, including that they must be targeted at the most at-risk groups including older adults,” said co-author Professor Sarah Gilbert.
“They must also be safe, effective in preventing disease and/or transmission, and provide at least six months of protection for people frequently exposed to the virus, such as healthcare workers.
“Our new study answers some of these questions about protecting older adults, but questions remain about effectiveness and length of protection, and we need to confirm our results in older adults with underlying conditions to ensure our vaccine protects those most at risk of severe COVID-19 disease.”
Almost all the participants were white and non-smokers, with the results therefore not necessarily applying to the general population.
Statistics have repeatedly flagged people of a non-white ethnicity are more likely to become seriously ill with the coronavirus and die. Smokers are also thought to be at greater risk.
The Oxford vaccine is now being tested in a phase 3 study, which usually involves a jab being given to thousands of people to uncover how effective it is.
The phase 3 participants are reportedly from a range of backgrounds, countries and ethnicities. Safety, efficacy and the optimal vaccine dose is also being tested on older adults with underlying health issues.
Writing in The Lancet, Dr Melissa Andrew from Dalhousie University in Canada – who was not involved in the Oxford research – said: “It is encouraging more studies in older adult populations are underway and will hopefully bring opportunities to implement nuanced analyses of how underlying health status and frailty affect vaccine safety, reactogenicity, immunogenicity, and efficacy in older adults in real-world settings.
“Older adults (across the full spectrum of frailty) and those who care about them are eagerly awaiting this progress towards safe and effective COVID-19 vaccines.”
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