Oxford COVID-19 Vaccine Found Adults Protected Against Disease
The Lancet published peer-reviewed, interim results of the Oxford COVID-19 vaccine (AZD1222) studies find that the vaccine protects against symptomatic disease in 70 percent of cases, with vaccine efficacy (VE) of 62 percent for those given 2 full doses.
Additionally, The Lancet disclosed on December 8, 2020, the VE was reported at 90 percent in those participants given a half, then a full dose (both trial arms pre-specified in the pooled analysis).
In summary, The Lancet article stated the ‘AZD1222 vaccine candidate was found to be safe, with only three out of 23,745 participants over a median of 3.4 months experiencing serious adverse events that were possibly related to a vaccine.
The Oxford COVID-19 vaccine uses a chimpanzee adenovirus viral vector that cannot cause disease in humans and expresses the SARS-CoV-2 coronavirus spike protein. This means the vaccine delivers the spike protein genetic code into vaccinated people's cells, producing the protein and teaching the immune system to recognize and attack the virus.
Past trial results have found that the vaccine induces antibody and T cell immune responses and is safe in adults aged 18 years and over, including older adults.
The trial was originally designed to assess a single dose of the vaccine, but following review of the immune response data in the UK phase 1/2 study (which found a second dose boosted immune responses), another dose was added to the trial protocol, then, once approved, second doses were given to participants.
Study author, Dr. Merryn Voysey, University of Oxford, UK, commented: "The results presented in this report provide the key findings from our first interim analysis. In future analyses, with more data included as it becomes available, we will investigate differences in key subgroups such as older adults, various ethnicities, doses, timing of booster vaccines, and we will determine which immune responses equate to protection from infection or disease."
The authors analyzed data from 23,745 adults in the UK, Brazil, and South Africa (11,730, 10,002, and 2,013 in each country, respectively) for the new study. The interim analysis pools the data providing greater precision for efficacy and safety outcomes than possible in individual trials and giving a broader understanding of the vaccine's use in different populations.
Participants in the COVID-19 vaccine group received 2-doses each containing 5x1010 viral particles (a standard dose).
However, a subset (1,367 people) in the UK received a half dose as their first dose, followed by a full second dose.
This was because of differences in the results of quantification methods between batches of the vaccine. The low-dose/standard-dose group did not include adults over the age of 55; the low-dose was given in an early stage of the trial before the recruitment of older adults had commenced.
The authors used the numbers of cases of symptomatic and asymptomatic infection to determine vaccine efficacy.
"To assess vaccine efficacy, we need to have a sufficient number of COVID-19 cases among participants to indicate that the vaccine is protecting them from the disease. Since the recruitment of older adults started later than in younger adults, there has been less follow-up time for these cohorts and less time to accrue COVID-19 cases.”
“This means we have to wait longer to have sufficient data to provide good vaccine efficacy estimates in smaller subgroups," added Dr. Voysey.
Overall, most participants were aged 18-55 years. In the 11,636 people included in the vaccine efficacy against symptomatic disease analysis, 12 percent were older adults, and most were white (83%).
The trial also measured protection against asymptomatic infection by asking 6,638 UK participants to complete weekly COVID tests. However, it is important to note these data are secondary outcomes, and findings need to be confirmed when there is more data available from the trial.
There were 69 cases of asymptomatic COVID-19 disease identified in the UK study's weekly COVID-19 testing of 6,638 people. This included 29/3,288 (0.9%) cases in the vaccine group and 40/3,350 (1.2%) cases in the control group.
In the low-dose/standard-dose group, there were 7/1,120 (0.6%) cases in the vaccine group and 17/1,127 (1.5%) cases in the control group.
In people given 2 standard doses, there were 22/2,168 (1%) cases in the vaccine group and 23/2,223 (1%) in the control group.
Co-author, Professor Sarah Gilbert, University of Oxford, UK, wrote: "Here we have shown for the first time that an adenoviral vectored vaccine - a type of vaccine technology which has been in use since 2009 - is efficacious and could contribute to disease control in the COVID-19 pandemic."
The authors note that they cannot assess the duration of protection, as the first trials were initiated in April 2020, and all disease episodes have accrued within 6-months of the first dose is administered. Further evidence will be required to determine the duration of protection and the need for additional booster doses of vaccine.
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