The AstraZeneca vaccine works similar to the Johnson & Johnson Covid-19 vaccine although it uses a simian (monkey virus) rather than human adenovirus, a respiratory tract infection virus, to carry the coronavirus spike protein to the immune system. This virus is deactivated and cannot cause an infection. A simian virus was chosen in case antibodies to human adenovirus prevented the vaccine from working well.
AstraZeneca and Oxford have made all severe reactions (viral infection of the spinal cord and pulmonary embolism) available early to the public prior to knowing whether or not they were vaccine-related. None of these were proven to be a result of the vaccine because the same percentages of cases were seen in individuals who did not receive the vaccine. A primary concern is that laboratory data show the vaccine did not create adequate immunity in the laboratory to the South African strain and South Africa stopped using this vaccine to vaccinate its population.
The FDA scientific subcommittees will look closely at all data in all populations for this vaccine and will be looking at the predictive percent of resistant strains in the United States to see if this vaccine will work and work safely in our population. I personally have seen these FDA committees in action and feel confident that their analysis is extremely careful and has the safety of the population in the United States as its foremost concern. It will be interesting to see the FDA final conclusions which will take several weeks.