The Oxford-AstraZeneca Covid-19 vaccine candidate has triggered a robust immune response in older adults in phase 2 clinical trials, demonstrating its potential usefulness in protecting a section of the population that is among the most at risk of illness from the novel coronavirus.
Preliminary findings published in The Lancet medical journal show ChAdOx1 nCov-2019 – technical name for the vaccine candidate developed by scientists at the University of Oxford and the British-Swedish pharma giant AstraZeneca – has been found to be safe, well-tolerated, and to produce a similar immune response across age groups after a boost vaccination.
Importantly, “ChAdOx1 nCoV-19 appears to be better tolerated in older adults than in younger adults…,” the study said – “and has similar immunogenicity across all age groups after a boost dose”.
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“Further assessment of the efficacy of this vaccine is warranted in all age groups and individuals with comorbidities,” the researchers said.
Dr Maheshi Ramasamy, an Investigator at the Oxford Vaccine Group, said, “Older adults are a priority group for Covid-19 vaccination, because they are at increased risk of severe disease, but we know that they tend to have poorer vaccine responses.
“We were pleased to see that our vaccine was not only well-tolerated in older adults; it also stimulated similar immune responses to those seen in younger volunteers. The next step will be to see if this translates into protection from the disease itself.”
These preliminary findings are significant for India, as this vaccine candidate is being put through phase 3 clinical trials in the country by Pune-based vaccine manufacturer Serum Institute India (SII) and Indian Council of Medical Research (ICMR). SII has already manufactured 40 million doses of the vaccine candidate under an at-risk manufacturing and stockpiling licence from the top national regulator, Drugs Controller General of India (DCGI), and will be supplying a large chunk of India’s domestic requirement for the vaccine.
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The findings reported in The Lancet (Safety and immunogenicity of ChAdOx1 nCoV-19 vaccine administered in a prime-boost regimen in young and old adults(COV002): a single-blind, randomised, controlled, phase 2/3 trial) brings hope that the vaccine will be able to help the large older adult population in the country against the virus.
Oxford researchers have said that “early efficacy readings” from ongoing phase 3 trials are “possible in the coming weeks”. Pfizer-BioNTech and Moderna have reported well over 90 per cent efficacy for their mRNA vaccine candidates in early results of phase 3 trials. The Russian Sputnik V candidate, manufactured by a lab based in Moscow, has also reported excellent phase 3 trial results. Although none of these studies have been peer-reviewed yet, hopes have risen of the imminent arrival of a shot that can defeat the virus that has sickened more than 56 million people and killed 1.35 million around the world so far.
During the phase 2 trial, the Oxford-AstraZeneca vaccine was evaluated in 560 healthy adult volunteers in the age groups of 18-55 years, 56-69 years, and 70 and older, who received either two doses of ChAdOx1 nCoV-19, or a placebo MenACWY vaccine.
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“Our findings show that the ChAdOx1 nCoV-19 vaccine was safe and well tolerated with a lower reactogenicity profile (ability to produce adverse reaction) in older adults than in younger adults. Immunogenicity (ability to generate immune response) was similar across age groups after a boost vaccination,” the study said.
“Most of the reported local and systemic adverse events” were mild to moderate in severity, the researchers said – in line with their previous phase 1 study. Serious adverse events observed during the trial “were judged to be unrelated to the study vaccines”, they said.
“Local and systemic reactions were more common in participants given ChAdOx1 nCoV-19 than in those given the control vaccine, and similar in nature to those previously reported (injection-site pain, feeling feverish, muscle ache, headache), but were less common in older adults (aged =56 years) than younger adults.
“The severity of symptoms reported in the standard-dose groups was reduced after the boost vaccination, with only one (1%) of 127 participants reporting a severe reaction compared with seven (5%) of 128 participants after the prime vaccination,” the study said.
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On detecting a pathogen, the human body produces two types of responses within the adaptive immune system: humoral or antibody-mediated immunity, and cellular immunity that occurs inside the infected cell and is mediated by T lymphocytes.
The vaccine candidate induced “specific antibody response” to the SARS-CoV-2 spike glycoprotein after a single dose across all age groups and, specifically, the neutralising antibody titres “after a boost dose were similar across all age groups”, the study said. The T-cell responses “peaked at 14 days after the prime vaccination”, it said.
“The robust humoral and cellular immune responses obtained in our older adult population were encouraging given that a number of studies have shown that decreasing immune function with age leads to decreased immune responses to vaccines.”
Dr Angela Minassian, Investigator at the University of Oxford and honorary consultant for infectious diseases, said: “Inducing robust immune responses in older adults has been a long-standing challenge in human vaccine research. To show this vaccine technology is able to induce these responses, in the age group most at risk from severe Covid-19 disease, offers hope that vaccine efficacy will be similar in younger and older adults.”
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