The vaccine being developed by the Oxford University (UK) and the AstraZeneca company against SARS-CoV-2, the virus that generates COVID-19, has shown similar safety and immunogenicity results in healthy older adults (56 years and older) to those seen in adults 18 to 55 years, according to a preliminary analysis published in the magazine ‘The Lancet’.
In this phase 2 trial, it has been determined thate vaccine causes few side effects and induces immune responses in both parts of the immune system in all age groups and at low and standard doses, eliciting a T-cell response within 14 days of the first dose of the vaccine (i.e., a cellular immune response, which could find and attack cells infected with the virus), and an antibody response within 28 days of the vaccine booster dose (i.e. a humoral immune response, which could find and attack the virus when it circulating in the blood or lymphatic system).
Now, phase 3 trials are underway to confirm these results, as well as the efficacy of the vaccine in the protection against SARS-CoV-2 infection, in a broader range of people, including older adults with underlying health problems.
‘Immune responses to vaccines tend to decline in older adults because the immune system gradually deteriorates with age, which also makes older adults more susceptible to infection. Thus, it is crucial that COVID-19 vaccines are tested in this group which is also a priority group for immunization‘Explains the study’s lead author, Professor Andrew Pollard of the University of Oxford.
‘The robust antibody and T-cell responses observed in older people in our study are encouraging. Populations most at risk for severe COVID-19 disease include people with existing health problems and older adults. We hope this means that our vaccine helps protect some of the most vulnerable people in society, but more research will be needed before we can be sure, “adds another author, Maheshi ramasamy, also from the University of Oxford.
In this phase 2 trial, 560 participants (160 aged 18 to 55, 160 aged 56 to 69, and 240 aged 70 and over) were divided into 10 groups in which they received the vaccine, called ChAdOx1 nCoV -19, in a low or standard dose, or a control vaccine (the meningococcal conjugate vaccine). Participants older than 55 years were also divided into groups and given a single dose of the vaccine, or two doses 28 days apart.
The study includes only healthy participants and not those with comorbidities or who are frail. Before receiving the vaccine, all participants had a blood test to determine if they had previously been infected with SARS-CoV-2. Those with antibodies were excluded, except for those 18 to 55 years of age in the standard double dose vaccine groups.
After vaccination, participants were observed for a minimum of 15 minutes for any immediate adverse events, and participants recorded any adverse events for the next seven days. Participants will continue to be monitored for any serious adverse events during the year following the final vaccination (data are not yet available throughout the year).
To participants 18 to 55 years of age who received two standard doses of Oxford COVID-19 vaccine and all participants aged 56 years or older had their immune response assessed on the day of vaccination, and then 1, 2, and 4 weeks after their first and second vaccinations.
Adverse reactions to the vaccine were mild (the most common effects were pain and tenderness at the injection site, fatigue, headache, fever, and muscle pain), but more common than those seen with the control vaccine. Thirteen serious adverse events occurred in the six months since the first dose was administered, none of which were related to any of the study vaccines.
Adverse effects were less common in older adults than in younger ones. Within seven days from a standard dose of ‘ChAdOx1 nCoV-19’ local symptoms such as temporary pain, tenderness, redness and swelling at the injection site occurred in 88 percent, 43/49 of 18 people to 55 years, 73 percent, 22/30 people 56 to 69 years and 61 percent, 30/49 people 70 years or older. At 7 days after injection, systemic symptoms such as temporary fatigue, headache, malaise, fever, and muscle aches occurred in 86 percent, 42/49 people aged 18 to 55, 77 percent, 23/30 people from 56 to 69 years and 65 percent, 32/49 people aged 70 and over.
Similar levels of local symptoms were seen after the first dose and the Oxford COVID-19 booster dose in older adults, while there were few systemic symptoms after the booster dose. The COVID-19 vaccine had similar immunogenicity in all age groups after a booster dose.
‘ChAdOx1 nCoV-19’ induced antibodies against SARS-CoV-2 spike protein and the receptor binding domain 28 days after a single low or standard dose in all age groups. After the booster dose of the vaccine, antibody levels increased on day 56 of the trial, regardless of the dose or age of the participants. The same was observed with neutralizing antibody levels on day 42, two weeks after the booster dose of the vaccine. At 14 days after the booster dose, 208 of the 209 (more than 99 percent) participants (selected from participants of all ages and doses) had neutralizing antibody responses.
T-cell responses against the SARS-CoV-2 spike protein peaked 14 days after the first vaccination, regardless of age and standard or low dose of the vaccine.
The authors note some limitations of their study, including that the participants in the oldest age group had a mean age of 73-74 years and few underlying health problems, so they may not be representative of the general elderly population , including people who live in residential care facilities or are over 80 years old.
Larger studies are currently underway to evaluate immunogenicity, safety, and efficacy in older adults with a broader range of comorbidities. Finally, the authors note that nearly all participants of all ages were white and non-smokers, and may not be representative of the general population, but people of diverse backgrounds are being included in the phase 3 trial of this vaccine. origins, countries and ethnicities.