Name: COVID-19 AstraZeneca Vaccine (AZD1222 or ChAdOx1 nCoV-19)

Type: Viral vector vaccine (chimpanzee adenovirus vector)

Developer: AstraZeneca

Recommended doses/interval: 2 doses, administered 12 weeks apart (noting a minimum interval of 4 weeks is acceptable)

Doses for Australia: 53.8 million doses, 3.8 million doses from overseas scheduled for delivery to Australia

Manufacturing: 50 million doses will be manufactured in Parkville, Australia in monthly batches by local biotechnology company, CSL

Storage: Can be stored, transported and handled at standard refrigerator temperatures (2-8°C)


The COVID-19 AstraZeneca vaccine utilises a chimpanzee adenovirus (ChAdOx1) vector; which is unable to cause disease in humans. This viral vector has been tested for safety in other vaccines for Ebola, Middle East respiratory syndrome (MERS) and influenza. This vaccine utilises the full length SARS-CoV-2 spike protein DNA inserted into the viral vector.

On 16 February 2021, COVID-19 AstraZeneca was granted provisional registration in Australia by the Therapeutic Goods Administration for use in those ≥ 18-years of age for the prevention of COVID-19 disease caused by SARS-CoV-2.

UPDATE: As of June 17th, 2021, following reported cases of thrombosis with thrombocytopaenia syndrome (TTS) after administration of the COVID-19 AstraZeneca, it is no longer the preferred vaccine for those aged < 60 years in Australia.

Clinical trials

Pre-clinical (animal) trials were conducted in rhesus macaques, mice and ferrets. These trials showed that there were no adverse safety events, no evidence of immune enhanced inflammatory disease and a balanced immune response was induced. In animals, the vaccine appeared to reduce disease severity, but did not prevent infection or transmission (nasal shedding of the virus still occurred).

Phase 1/2 clinical trials were conducted in UK and recruited over one thousand participants in April and May 2020. Phase 2/3 clinical trials are being conducted in 50,000 participants globally (UK, USA, Brazil, South Africa and Kenya), with recruitment starting in July 2020.

Interim results of Phase 3 studies, from over 10,000 participants in the UK, Brazil and South Africa, were published in the Lancet on 8 December 2020. In participants who received two standard doses, vaccine efficacy was 62·1% and in participants who received a low dose followed by a standard dose, efficacy was 90%. Overall vaccine efficacy across both groups was 70·4%.

Primary results from a further phase 3 US trial including 32,449 participants were released by AstraZeneca on 22 March 2021. The vaccine demonstrated efficacy of 76% against symptomatic disease and 100% efficacy against severe or critical disease and hospitalisation. These results were consistent across age groups, with vaccine efficacy of 85% in people aged over 65-years. These results are currently undergoing peer review.

Safety profile

Phase 1/2 results showed that the vaccine was safe but had higher reactogenicity than the control vaccine. Symptoms mainly occurred in the day following vaccination and self-resolved. Pain and tenderness at the injection site (83%), fatigue (68%) and headache (70%) were the most common symptoms in participants receiving COVID-19 AstraZeneca. Fever occurred in 18% and flu-like symptoms of malaise (61%) and muscle ache (60%) were also common.

Phase 2/3 results showed similar reactions to those seen in Phase 1/2 trials but reactions were less common in older adults (aged over 55-years) and after the second dose. Most of the reported local and systemic adverse events were mild to moderate in severity.

Of the nearly 24,000 trial volunteers, only three of the 175 reported serious adverse events were possibly related to the vaccine and more than half of these events occurred in the control arm.

There have been two trial pauses due to initially unexplained illnesses; these were reviewed by independent experts before restarting the trials. One case of transverse myelitis was reported two weeks after COVID-19 AstraZeneca booster vaccination and was possibly related to vaccination. There were two additional cases of transverse myelitis that were determined to be unlikely to be related to vaccination by an independent committee of neurological experts. One case was due to pre-existing, but previously unrecognised, multiple sclerosis and the second case occurred in the control arm.

Primary results from the Phase 3 US trial showed that the COVID-19 AstraZeneca was well tolerated, and no safety concerns related to the vaccine were identified. The results are currently undergoing peer review.

Post-licensure surveillance

An independent expert review of 7 reported cases in Australia of suspected anaphylaxis following administration of the COVID-19 AstraZeneca vaccine has concluded that there is no increased risk of anaphylaxis associated with the vaccine above the expected rate for any other vaccine. Anaphylaxis is a very rare side effect that can occur with any vaccine.

Thrombosis with thrombocytopenia syndrome (TTS), is a rare and new syndrome which has been reported in people who have received an adenoviral vector COVID-19 vaccine (eg. Johnson & Johnson/Janssen and COVID-19 AstraZeneca).

The syndrome is distinct from other clotting conditions as it is characterised by thrombosis formation (blood clots) combined with thrombocytopenia (low platelet levels).  Symptoms occur 4-30 days following vaccination. Early recognition can lead to effective treatment.


Authors: Daniela Say (MVEC Immunisation Fellow) and Nigel Crawford (Director SAEFVIC, Murdoch Children’s Research Institute)

Reviewed by: Daryl Cheng (Paediatrician, Royal Children’s Hospital), Davina Buntsma (MVEC Immunisation Fellow), Rachael McGuire (MVEC Education Nurse Coordinator) and Francesca Machingaifa (MVEC Education Nurse Coordinator)

Date: 17th June 2021

Materials in this section are updated as new information and vaccines become available. The Melbourne Vaccine Education Centre (MVEC) staff regularly reviews materials for accuracy.

You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family’s personal health. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult a healthcare professional.