Study results published in The Lancet suggest that the chimpanzee adenovirus-vectored COVID-19 vaccine being developed by AstraZeneca and the University of Oxford is able to produce a strong immune response in older adults, whilst being better tolerated in this age group than compared with younger adults. Data on the effects of AZD1222, also known as ChAdOx1 nCoV-19, among older people were preliminarily reported last month.
The latest analysis comes from the phase 2 portion of the ongoing phase 2/3 trial that has enrolled healthy adults aged 18 years and older. The analysis includes a total of 560 participants, with 160 aged 18 to 55 years, 160 aged 56 to 69 years and 240 aged 70 years and older. The subjects were randomized to receive either AZD1222 or a control vaccine at various doses and schedules, with prime-booster regimens given 28 days apart.
The researchers noted that the main objectives of the current analysis were to assess safety, as well as the humoral and cellular immunogenicity of a single-dose and two-dose schedule in adults older than 55 years. The co-primary outcomes of the trial are efficacy, as measured by the number of cases of symptomatic, virologically confirmed COVID-19, and safety, as measured by the occurrence of serious adverse events.
Immune response comparable across age groups
Results showed that in participants who received two doses of AZD1222, median anti-spike SARS-CoV-2 IgG responses 28 days after the boost dose were similar across the three age cohorts, while neutralizing antibody titres after a boost dose were also similar across the groups. Further data indicated that 14 days after the boost dose, 208 of 209 participants that received the second vaccination had neutralizing antibody responses. Meanwhile, T-cell responses peaked at day 14 after a single standard dose of AZD1222 in all age groups.
“The robust antibody and T-cell responses seen in older people in our study are encouraging,” said Maheshi Ramasamy, co-lead investigator at the Oxford Vaccine Group, adding “the next step will be to see if this translates into protection from the disease itself.”
Local, systemic reactions lower in older adults
With regards safety, in people given the two standard doses of AZD1222, after the prime vaccination local reactions were reported in 88% of those in the 18 to 55 years group, 73% of subjects in the 56 to 69 years group and 61% in the 70 years and older group. Further, systemic reactions occurred at rates of 86%, 77% and 65%, respectively.
Efficacy results expected imminently
Andrew Pollard, chief trial investigator, indicated that “high-level” efficacy results on AZD1222 are expected in the coming weeks from an ongoing phase 3 study, with the analysis triggered after there have been 53 confirmed cases of COVID-19 among participants. “We’re getting close, and it’s definitely going to be before Christmas, based on the progress,” Pollard remarked.
Pollard also suggested that there was “no competition” with other vaccines, as “we will need all of them to protect people around the globe.” This week, Pfizer and BioNTech released data from the final efficacy analysis of a phase 3 study of BNT162b2, with their mRNA-based COVID-19 vaccine candidate demonstrating an efficacy rate of 95%. Prior to this, Moderna reported that its experimental COVID-19 vaccine mRNA-1273 showed an efficacy rate of 94.5% in the first interim analysis of the phase 3 COVE study.