The UK’s leading Covid-19 vaccine trial shows that the elderly tolerate the shot better than younger adults.
The findings from the second phase of the trials, published in The Lancet medical journal on Thursday, show that the vaccine is "safe and provokes immune response".
Research has already revealed that older adults are more susceptible to catching severe cases of the virus and scientists behind the trials said that the vaccine – created by AstraZeneca in partnership with the University of Oxford – produces a similar immune response in old and young adults.
However, signs of potential side-effects were found in the young rather than in older recipients.
Adverse reactions to the inoculation were mild, the most common being pain and tenderness at the point of injection, fatigue, headache, fever and muscle pain.
"Adverse effects were less common in older adults than in younger adults," The Lancet report said.
“The robust antibody and T-cell responses seen in older people in our study are encouraging,” said the report’s co-author, Dr Maheshi Ramasamy, of the University of Oxford.
“The populations at greatest risk of serious Covid-19 disease include people with existing health conditions and older adults.
“We hope 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.”
More than 560 healthy adults took part in the trial, including 240 people over the age of 70, during the UK’s first lockdown this year.
The vaccine shows "similar safety and immunogenicity results in healthy older adults to those seen in adults aged 18-55 years", according to The Lancet.
The journal said that the vaccine caused “few side effects” and induces an immune response in all age groups within 14 days of the first dose and an antibody response within 28 days of a booster dose.
Researchers say that the third phase of the trial is ongoing and will examine the effect on older adults with underlying health conditions.
“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,” said Prof Andrew Pollard, the study’s lead author.
"As a result, it is crucial that Covid-19 vaccines are tested in this group who are also a priority group for immunisation."
The new study is the fifth published clinical trial of a vaccine against Covid tested on an older adult population.
Other shots were also shown to generate an immune response in older adults.
“The World Health Organisation 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 Prof 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 that our vaccine protects those most at risk of severe Covid-19 disease.”
The authors said further research was required to ensure that people from a range of backgrounds, countries and ethnicities were tested.
Candidates in the trial were almost all from white backgrounds and were non-smokers.