According to the information that AstraZeneca and the University of Oxford presented to the United Kingdom's vaccine regulatory agency, this vaccine contains:

• A weakened adenovirus, which delivers the the COVID-19 spike glycoprotein (this is the active ingredient; also called the 'antigen')
• L-histidine (amino acid)
• L-histidine hydrochloride monohydrate (amino acid)
• Magnesium chloride hexahydrate (salt)
• Polysorbate 80 (surfactant)
• Ethanol (alcohol)
• Sucrose (sugar)
• Sodium chloride (salt)
• Disodium edetate dihydrate (salt)
• Water for injections (diluent)

The vaccine does not include any human or animal products, thimerosal, gelatin, or formaldehyde. The vaccine doesn't include any common allergens like egg, latex, milk, gluten, lactose, maize/corn, or peanuts, either.

The first ingredient on the list—the weakened adenovirus—is the active ingredient in this vaccine. Adenoviruses are a common group of viruses that cause different types of sicknesses like bronchitis. Most people have been exposed to them in their lives. The AstraZeneca vaccine is made from an adenovirus that has been changed in the lab so it can't cause harm. It has been adjusted to work as a delivery system for the vaccine. The shot gives the body instructions to create the spike protein from COVID-19 in its cells. That way, when a person is exposed to COVID-19, its immune system will recognize the part of the virus that has those spike proteins and will know how to how to fight it.

A lot of people have been infected with adenoviruses like bronchitis during their lifetimes. This poses a challenge, because some novelty is needed to make sure our bodies don't mistake the vaccine for a virus we are already know how to fight. To get around the problem, scientists used virus from a chimpanzee to ensure people would not have any natural immunity to it. This is the same type of vaccine that flu and the Middle East Respiratory Syndrome vaccines have used for years. It is a proven, safe and relatively old approach.

The last nine ingredients on the list are called 'excipients.' Excipients are the non-active ingredients that are added to the vaccine for a variety of reasons.

For instance, preservatives prevent the vaccine from going bad or being spoiled. Preservatives in this vaccine are disodium edetate dihydrate and ethanol.

Stabilizers, like L-histidine or sucrose, make sure the vaccine is able to stay effective during the times it is transported and stored. 

Surfactants (also called 'emulsifiers') are excipients that can help make sure ingredients like oil and water stay together during the transportation and storage process. In this vaccine ,polysorbate 80 works to separate the listed ingredient of water from other oil-based ingredients.

Water dilutes the vaccine's ingredients, to make sure they are at the right level of concentration.

Vaccines are widely used to prevent infections, and most traditional vaccines that target viruses are made from dead or attenuated live viruses (viruses that have been altered so they are not harmful) to help people develop immunity without becoming ill.

Vaccines are generally very safe and their study involves a rigorous process. Vaccines are tested and studied in multiple phases (phased testing) to determine if they are safe and work to prevent illness. Before a vaccine is tested on humans, in the preclinical phase it is tested on laboratory cells or animals.

Once it is approved for human research, there are three phases that take place before the vaccine can be considered for approval for public use. During the first stage (Phase I), the new vaccine is provided to small groups of people—the first time the vaccine is tested in humans. The second stage (Phase II) involves testing the vaccine on people who have similar characteristics (such as age and physical health) to the target population, or the group for which the vaccine is intended. The goal of this stage is to identify the most effective dosages and schedule for Phase III trials. The final stage (Phase III) provides the vaccine to thousands of people from the target population to see how safe and effective it is. Once the vaccine has undergone Phase 3 testing, the manufacturer can apply for a license from regulatory authorities (like the FDA in the US) to make the vaccine available for public use. Once approved, the drugmaker will work with national governments and international health organizations to monitor vaccine recipients for potential side effects from the vaccine that were not seen in clinical trials (this is called surveillance). This phase also helps researchers understand how well a vaccine works over a longer time frame and how safe it is for the population.