On February 26th, Health Canada officially approved the Oxford-AstraZeneca vaccine (called ChAdOx1) following clinical trials that displayed a 62.1% efficacy rate in reducing symptomatic cases of COVID-19. Health Canada’s approval followed a series of national regulators authorizing the vaccine for administration across the EU, the UK, India and Mexico.
Through a global vaccine-sharing initiative called COVAX, Canada has plans to purchase 1.9-3.2 million doses in addition to an agreement with AstraZeneca to buy 20 million doses of the vaccine. Canada also plans to purchase approximately 2 million doses of the vaccine manufactured by the Serum Institute of India. Despite the relatively lower efficacy rate of the Oxford-AstraZeneca vaccine, the approval was a welcome response to Canada’s attempts to ramp up vaccine rollout in the wake of new emerging variants.
Clinical Trials
The Oxford-AstraZeneca vaccine prevents COVID-19 in adults (age 18 years and older). Clinical trials are currently underway to evaluate the effectiveness of the vaccine in preventing symptomatic cases in children and young adults (below 18 years of age). During clinical trials, 64 of the 5,258 individuals in the group who had received the vaccine developed symptoms compared with 154 of 5,210 individuals who developed symptoms in the control group.
The dominant age group participating in the clinical trials were mostly between the ages of 18 and 55 years old; with limited information on the effectiveness of the vaccine in individuals 55 years or older. However, given the anticipated immune response during trials, protection is expected for individuals 55 years or older. Health Canada regulators further emphasized that overall, there were “no important safety concerns, and the vaccine was well-tolerated by participants.”
How Does it Work?
Similar to Moderna and Pfizer-BioNTech’s vaccine, the Oxford-AstraZeneca vaccine is administered through two doses, with the second dose following four to twelve weeks after the first administration. In contrast to Moderna and Pfizer’s mRNA vaccines, the Oxford AstraZeneca vaccines follows a more conventional approach to vaccine development by preparing the body to defend itself against COVID-19.
While mRNA vaccines deliver RNA that encodes the spike protein on the surface of the SARS-CoV-2 virus, the Oxford-AstraZeneca vaccine utilizes an adenovirus, modified to contain the gene encoding the SAR-CoV-2 spike protein. The spike protein is a large transmembrane protein which assembles to form the “corona”, or crown-like appearance, which the virus needs to enter into the body’s cells. Once the vaccine delivers the SARS-CoV-2 gene into the cells, the cells will use the gene to produce the spike protein.
Vaccines based on the spike protein have sought to induce antibodies to block the virus from binding and fusing to the body’s cells. Upon first introduction to the virus through vaccine administration, the individual’s immune system will produce antibodies and activate white blood cells (T cells) to attack. When an individual is subsequently exposed to the SARS-CoV-2 virus, the immune system will be able to recognise the virus and effectively defend the body from reinfection.
Efficacy vs Distribution:
It is important to note that despite the lower efficacy rate of the Oxford-AstraZeneca vaccine, the vaccine is 100% effective in preventing severe cases of COVID-19, including hospitalizations and death. Notably, the Oxford-AstraZeneca vaccine has a higher efficacy rate than common vaccine products, including flu vaccines which typically range from 54-64% effective against seasonal influenza.
Additionally, with regards to the logistics of distribution, the Oxford-AstraZeneca vaccine may be stored, transported, and handled at normal refrigerated conditions, in stark contrast to the ultra-cold storage required to preserve the Moderna and Pfizer vaccines. With the ease of storage and transportation, the vaccine may be distributed at a faster pace and on a broader scale – with the potential for the vaccine to be widely circulated across remote regions of Canada and the world.
While Health Canada is still in the process of reviewing other vaccine candidates (in particular; the Johnson & Johnson and Novavax vaccines), it is clear that there are inherent advantages in having multiple vaccine candidates available for distribution. This is particularly the case as Canada stands as a vaccine laggard in the Western world with only 4.5% of the population vaccinated and 1.68 million shots administered as of February 25. As Canada seeks to ramp up its vaccine distribution and inoculation efforts in attempts to vaccinate as many people as possible, multiple vaccine candidates provide a welcome safety net in a race against time with rapidly emerging COVID-19 variants.