The AstraZeneca vaccine is a viral vector vaccine (external link). Unlike the Pfizer-BioNTech and Moderna vaccines which store the instructions to build spike proteins in RNA, the AstraZeneca vaccine uses DNA. The vaccine uses a harmless virus (called an adenovirus) as a delivery system. This is called a viral vector. Once the vaccine containing the viral vector enters the body, the vector virus produces the SARS-CoV-2 spike protein. Just like with the mRNA vaccines, the immune system responds to the spike proteins by making antibodies. These new antibodies will break down the spike proteins and get rid of them. The new antibodies will protect against COVID-19 infection in the future.
DNA is not as fragile as RNA. The viral vector (adenovirus) has a tough protein coat which protects the DNA inside. Therefore, the AstraZeneca vaccine does not need to be kept frozen.
Viral vector technology has been used for over ten years to produce many of the vaccines approved in Canada.
None of the COVID-19 vaccines currently approved by Health Canada use the live virus that causes COVID-19. You cannot get COVID-19 from a vaccine.