These COVID-19 vaccine FAQs have been designed to address common queries relating to Vaxzevria (AstraZeneca).

Please also see our other COVID-19 FAQs for more information on other COVID-19 related topics:

For ease of reference, information has been categorised as per the below themes:

This page will be updated on a regular basis as further information becomes available regarding COVID-19 vaccines.

For questions that have not been addressed on this page or our dedicated COVID-19 resource page, please contact us here.

Thrombosis with thrombocytopenia (TTS)

  • What is thrombosis with thrombocytopenia syndrome?

    Thrombosis with thrombocytopenia syndrome, 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 Vaxzevria (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.

  • What is the difference between Tier 1 and Tier 2 thrombosis with thrombocytopenia syndrome (TTS)?

    Tier 1 and Tier 2 definitions have been applied to TTS by the CDC (Centers for Disease Control and Prevention) in the United States. The tiers are defined by the following:

    Tier 1:

    • unusual site of thrombosis (e.g neurological – central venous sinus thrombosis [CVST] or gut – eg splanchnic vein, associated with bowel ischaemia and surgery, portal vein or other rare venous and arterial thromboses)
    • Platelet count <150,000 per microliter
    • Positive (+) heparin-P4 ELISA HIT antibody result is supportive, but not required

    Tier 2:

    • Usual sites of thrombosis such as leg or lungs (eg. venous thromboembolism, deep vein thrombosis, pulmonary embolism)
    • Platelet count <150,000 per microliter
    • Positive (+) heparin-P4 ELISA HIT antibody result is required

    Tier 1 is more severe, with higher morbidity and mortality than Tier 2. Evidence is emerging that Tier 1 is more common in younger age groups, hence the preferential recommendation for alternative vaccines (in Australia, Vaxzevria (AstraZeneca) is not the preferred vaccine for people aged < 60 years – see the Joint statement from ATAGI and THANZ on Thrombosis with Thrombocytopenia Syndrome (TTS) and the use of COVID-19 Vaccine AstraZeneca for further information).

  • Are there any risk factors for developing thrombosis with thrombocytopenia syndrome (TTS)? eg. age, gender etc

    There have been no known markers identified that either increase or decrease an individual’s risk of developing TTS. This includes having a past history of clots in the leg (DVT), lungs (pulmonary embolus) or heart (myocardial infarction).

    Evidence thus far indicates there is a higher risk of TTS in the younger population (< 60 years of age), although there has been a small number of cases identified in older adults.

  • When do symptoms of thrombosis with thrombocytopenia syndrome (TTS) occur?

    Symptoms of TTS have been reported to occur in the 4-30 day time period following administration of a COVID-19 adenoviral vector vaccine (eg. Johnson & Johnson/Janssen or Vaxzevria (AstraZeneca)). Current information suggests that the risk of TTS is much lower following receipt of a second dose.

    Symptoms can include

    • Cerebral venous sinus thrombosis (CVST): persistent headaches (unresponsive to simple analgesia), visual changes, focal neurological symptoms (e.g. movement or sensation changes), seizures, coma, secondary intra-cerebral haemorrhage, confusion, encephalopathy
    • Splanchnic vein thrombosis: abdominal pain
    • Pulmonary embolus: chest pain/significant respiratory symptoms or distress, dyspnoea
    • Deep vein thrombosis: leg pain, redness or swelling
    • Arterial ischaemia: pallor and coldness in limb, myocardial ischaemia
    • Thrombocytopenia: acute onset bruising or bleeding, petechial rash

    NB: These symptoms are different from the common or expected side effects following vaccination which usually occur in the first 24-48 hours and last 1-2 days.

  • I am over 60 years of age and have a history of deep vein thrombosis (DVT’s). Is it safe for me to receive the Vaxzevria (AstraZeneca) vaccine?

    There is currently no evidence to suggest that having a history of DVT’s or other general thromboembolic disorders predisposes you to developing thrombosis with thrombocytopenia syndrome (TTS) following receipt of an adenoviral vector vaccine such as Vaxzevria (AstraZeneca). In contrast, there is strong evidence that COVID-19 disease is thrombogenic (promotes clot development) and may cause a variety of thromboembolic events. TTS is a unique condition involving the development of thromboses (blood clots) combined with thrombocytopenia (low platelets).

    Individuals with a history of DVT’s are encouraged to receive a COVID-19 vaccine when offered.

    Refer to the Joint statement from ATAGI and THANZ on Thrombosis with Thrombocytopenia Syndrome (TTS) and the use of COVID-19 Vaccine AstraZeneca for more information.

  • I am taking hormone replacement therapy. Am I at an increased risk of thrombosis with thrombocytopenia syndrome (TTS) if I am given Vaxzevria (AstraZeneca)?

    There is currently no evidence to suggest that taking certain medications or being prone to developing blood clots puts you at increased risk of developing TTS following receipt of Vaxzevria (AstraZeneca). In contrast, there is strong evidence that COVID-19 disease is thrombogenic (promotes clot development) and may cause a variety of thromboembolic events. TTS is a unique condition involving the development of thromboses (blood clots) combined with thrombocytopenia (low platelets).

    Individuals who are taking hormone replacement therapy are encouraged to receive a COVID-19 vaccine when it is offered.

    For more information please refer to: Joint statement from ATAGI and THANZ on Thrombosis with Thrombocytopenia Syndrome (TTS) and the use of COVID-19 Vaccine AstraZeneca.

  • I am over 60 years of age and have a history of atrial fibrillation putting me at a higher risk of blood clots. Is it safe for me to have Vaxzevria (AstraZeneca)?

    There is currently no evidence to suggest that having a medical condition which increases your likelihood of developing blood clots puts you at a greater risk of developing TTS following receipt of Vaxzevria (AstraZeneca).

    There is currently no evidence to suggest that having a history of atrial fibrillation predisposes you to developing thrombosis with thrombocytopenia syndrome (TTS) following receipt of an adenoviral vector vaccine such as Vaxzevria. In contrast, there is strong evidence that COVID-19 disease is thrombogenic (promotes clot development) and may cause a variety of thromboembolic events. TTS is a unique condition involving the development of thromboses (blood clots) combined with thrombocytopenia (low platelets).

    Individuals with a history of atrial fibrillation are encouraged to receive a COVID-19 vaccine when offered.

    Refer to the Joint statement from ATAGI and THANZ on Thrombosis with Thrombocytopenia Syndrome (TTS) and the use of COVID-19 Vaccine AstraZeneca for more information.

  • What is the risk-benefit ratio (also known as benefit-risk assessment) when weighing up whether to get vaccinated?

    A benefit-risk assessment is important to conduct when recommending any vaccination. This measures the benefits of vaccination (eg. reduction of morbidity and mortality from the disease) to any potential risks. Also known as a benefit-risk ratio or balance, it will vary with other factors such as age, prevalence of outbreaks in a population and potential exposure to the disease in their workplace. This assessment may differ from individual to individual.

    For COVID-19, older people are at an increased risk of severe disease and death if they contract COVID-19. Younger people with underlying conditions such as immunocompromise, are also at an increased risk of severe disease, which affects their benefit-to-risk balance.

    The absence of COVID-19 in the community also affects this benefit-to-risk balance. Current advice would be reconsidered in the context of an outbreak, as the benefit in preventing COVID-19 would outweigh the risk for most adults.

    For more information on weighing up the potential benefits vs risk of harm please refer to Weighing up the potential benefits against risk of harm from COVID-19 AstraZeneca.

    Whilst the current recommendations in Australia are that Comirnaty (Pfizer) is preferred vaccine for people under 60, a person in this age group can make an informed decision in conjunction with their healthcare provider to receive a Vaxzevria (AstraZeneca) vaccine based on an understanding of their individual benefit-risk assessment.

  • ATAGI have noted that “people of any age without contraindications who have had their first dose of Vaxzevria (AstraZeneca) vaccine without any serious adverse events should receive a second dose of the same vaccine``. What constitutes a serious adverse event?

    A serious adverse event following immunisation (AEFI) includes anaphylaxis or thrombosis with thrombocytopenia syndrome (TTS).

    Anaphylaxis to a previous dose of a vaccine is a contraindication to future doses of that same vaccine.

    As a precaution those with a past history of TTS, cerebral venous sinus thrombosis (CVST), heparin-induced thrombocytopenia (HIT), idiopathic splanchnic (mesenteric, portal and splenic) venous thrombosis, anti-phospholipid syndrome (with thrombosis and/or miscarriage), or capillary leak syndrome are advised not to receive Vaxzevria (AstraZeneca).

    All adverse events should be reported to SAEFVIC. Specialist immunisation advice can be sought by referring patients to the VicSIS.

Allergies

  • ATAGI have noted that “people of any age without contraindications who have had their first dose of Vaxzevria (AstraZeneca) vaccine without any serious adverse events should receive a second dose of the same vaccine``. What constitutes a serious adverse event?

    A serious adverse event following immunisation (AEFI) includes anaphylaxis or thrombosis with thrombocytopenia syndrome (TTS).

    Anaphylaxis to a previous dose of a vaccine is a contraindication to future doses of that same vaccine.

    As a precaution those with a past history of TTS, cerebral venous sinus thrombosis (CVST), heparin-induced thrombocytopenia (HIT), idiopathic splanchnic (mesenteric, portal and splenic) venous thrombosis, anti-phospholipid syndrome (with thrombosis and/or miscarriage), or capillary leak syndrome are advised not to receive Vaxzevria (AstraZeneca).

    All adverse events should be reported to SAEFVIC. Specialist immunisation advice can be sought by referring patients to the VicSIS.

  • I am under 60 years of age and allergic to Polyethylene Glycol (PEG) which is an ingredient in Comirnaty (Pfizer) and Spikevax (Moderna). Can I/should I receive Vaxzevria (AstraZeneca)?

    PEG is an ingredient contained in Comirnaty (Pfizer) and Spikevax (Moderna) and it is therefore recommended that you are referred to an immunology/allergy/vaccination specialist for immunisation advice.

    NB: Vaccination with Comirnaty or Spikevax is contraindicated in people with documented anaphylaxis to PEG.

    For more information refer to MVEC: COVID-19 vaccines and allergy or COVID-19 vaccination – ATAGI clinical guidance on COVID-19 vaccine in Australia in 2021

General questions

  • I am under 60 years of age and have had dose 1 of Vaxzevria (AstraZeneca), is it safe to receive dose 2?

    People who have received their first dose of Vaxzevria (AstraZeneca) without any serious adverse events can receive their second dose. This should be done in the recommended time frame of 4-12 weeks between doses. Current information suggests that thrombosis with thrombocytopenia syndrome is more frequently reported following receipt of dose 1 of Vaxzevria.

    For more information refer to ATAGI statement on revised recommendations on the use of COVID-19 Vaccine AstraZeneca.

  • I am under 60 years of age and received Vaxzevria (AstraZeneca) as my first dose, should I/can I have Comirnaty (Pfizer) or Spikevax (Moderna) as my dose 2 of a COVID-19 vaccine? Or now commence a course of 2 doses of Comirnaty/Spikevax and no further doses of Vaxzevria?

    Combined or mixed COVID-19 vaccine schedules are not routinely recommended in Australia. Clinical trials involving mixed vaccine schedules are currently underway to provide more information relating to safety and efficacy, as well as information on the appropriate intervals between doses. Current information suggests that thrombosis with thrombocytopenia syndrome (TTS) is rarely reported following receipt of dose 2 of adenoviral vector vaccines. If a person has received the first dose of Vaxzevria (AstraZeneca) without any serious adverse events such as TTS or anaphylaxis, then they can receive the second dose.

  • I am over 60 years of age and have a history of deep vein thrombosis (DVT’s). Is it safe for me to receive Vaxzevria (AstraZeneca) vaccine?

    There is currently no evidence to suggest that having a history of DVT’s or other general thromboembolic disorders predisposes you to developing thrombosis with thrombocytopenia syndrome (TTS) following receipt of an adenoviral vector vaccine such as Vaxzevria (AstraZeneca). In contrast, there is strong evidence that COVID-19 disease is thrombogenic (promotes clot development) and may cause a variety of thromboembolic events. TTS is a unique condition involving the development of thromboses (blood clots) combined with thrombocytopenia (low platelets).

    Individuals with a history of DVT’s are encouraged to receive a COVID-19 vaccine when offered.

    Refer to the Joint statement from ATAGI and THANZ on Thrombosis with Thrombocytopenia Syndrome (TTS) and the use of COVID-19 Vaccine AstraZeneca for more information.

  • I am under 60 years of age and travelling to an area experiencing a current COVID-19 outbreak. Should I have the Vaxzevria (AstraZeneca) vaccine as I am unable to source an alternative?

    ATAGI recommends that Vaxzevria (AstraZeneca) can be administered in adults aged under 60 years of age where the benefits of protection are likely to outweigh the risks of vaccination for that individual. It is important to discuss your individual circumstances with a health care provider in order to make an informed decision. There may be some differences to this advice depending on the state/jurisdiction you live in, so please check with your local Department of Health.

    To read more refer to ATAGI statement on revised recommendations on the use of COVID-19 Vaccine AstraZeneca and ATAGI statement on use of COVID-19 vaccines in an outbreak setting.

  • I am taking hormone replacement therapy. Am I at an increased risk of thrombosis with thrombocytopenia syndrome (TTS) if I am given Vaxzevria (AstraZeneca) vaccine?

    There is currently no evidence to suggest that taking certain medications or being prone to developing blood clots puts you at increased risk of developing TTS following receipt of Vaxzevria (AstraZeneca) vaccine.  In contrast, there is strong evidence that COVID-19 disease is thrombogenic (promotes clot development) and may cause a variety of thromboembolic events. TTS is a unique condition involving the development of thromboses (blood clots) combined with thrombocytopenia (low platelets).

    Individuals who are taking hormone replacement therapy are encouraged to receive a COVID-19 vaccine when it is offered.

    For more information please refer to: Joint statement from ATAGI and THANZ on Thrombosis with Thrombocytopenia Syndrome (TTS) and the use of COVID-19 Vaccine AstraZeneca.

  • I am over 60 years of age and have a history of atrial fibrillation putting me at a higher risk of blood clots. Is it safe for me to have Vaxzevria (AstraZeneca) vaccine?

    There is currently no evidence to suggest that having a medical condition which increases your likelihood of developing blood clots puts you at a greater risk of developing TTS following receipt of Vaxzevria (AstraZeneca) vaccine.

    There is currently no evidence to suggest that having a history of atrial fibrillation predisposes you to developing thrombosis with thrombocytopenia syndrome (TTS) following receipt of an adenoviral vector vaccine such as Vaxzevria. In contrast, there is strong evidence that COVID-19 disease is thrombogenic (promotes clot development) and may cause a variety of thromboembolic events. TTS is a unique condition involving the development of thromboses (blood clots) combined with thrombocytopenia (low platelets).

    Individuals with a history of atrial fibrillation are encouraged to receive a COVID-19 vaccine when offered.

    Refer to the Joint statement from ATAGI and THANZ on Thrombosis with Thrombocytopenia Syndrome (TTS) and the use of COVID-19 Vaccine AstraZeneca for more information.

  • I am under 60 years of age and I just want to be vaccinated ASAP. Can I have Vaxzevria (AstraZeneca) as it is more readily available?

    Whilst alternate COVID-19 vaccine brands (Comirnaty (Pfizer) or Spikevax (Moderna)) are preferred for individuals aged 18-59 years, Vaxzevria (AstraZeneca) is not contraindicated in this group. In the setting of a COVID-19 outbreak, it is recommended that individuals assess the benefits to them and their contacts of receiving any vaccine compared with the risk of developing rarer side effects.

  • I am 61 years of age. Why is Vaxzevria (AstraZeneca) vaccine deemed safe for me to receive?

    Like any arbitrary age cut-off, it is acknowledged that there may be limited difference between an individual at age 60 or 61 years. What we do know is that the risk of intensive care admissions and death increases markedly with age, with each decade of life increasing the risk 3-fold. Conversely, the possibility of thrombosis with thrombocytopenia syndrome (TTS) may be higher in younger people, based on currently available data.

    ATAGI have taken this data, along with safety data analysis from other countries such as the UK, other risks such as prevalence of COVID-19 in the Australian population along with any existing COVID-19 outbreaks, to calculate an age-specific benefit-to-risk balance for the Australian population. This has resulted in a current age cutoff of 60 years old in the current recommendations.

  • What is the risk-benefit ratio (also known as benefit-risk-assessment) when weighing up whether to get vaccinated?

    A benefit-risk assessment is important to conduct when recommending any vaccination. This measures the benefits of vaccination (eg. reduction of morbidity and mortality from the disease) to any potential risks. Also known as a benefit-risk ratio or balance, it will vary with other factors such as age, prevalence of outbreaks in a population and potential exposure to the disease in their workplace. This assessment may differ from individual to individual.

    For COVID-19, older people are at an increased risk of severe disease and death if they contract COVID-19. Younger people with underlying conditions such as immunocompromise, are also at an increased risk of severe disease, which affects their benefit-to-risk balance.

    The absence of COVID-19 in the community also affects this benefit-to-risk balance. Current advice would be reconsidered in the context of an outbreak, as the benefit in preventing COVID-19 would outweigh the risk for most adults.

    For more information on weighing up the potential benefits vs risk of harm please refer to Weighing up the potential benefits against risk of harm from COVID-19 AstraZeneca.

    Whilst the current recommendations in Australia are that Comirnaty (Pfizer) and Spikevax (Moderna) are the preferred vaccines for people under 60 years, a person in this age group can make an informed decision in conjunction with their healthcare provider to receive Vaxzevria (AstraZeneca) based on an understanding of their individual benefit-risk assessment.

  • Can I get a blood test to check my immune response from the first dose and avoid the need for a second dose?

    COVID-19 serology is not routinely available following vaccination and is not able to inform the decision to proceed with future doses. Due to the novel nature of SARS-CoV-2, a correlate of protection has not yet been established for COVID-19 in humans.

    Data from clinical trials demonstrated that a 4-12 week interval between 2 doses of Vaxzevria (AstraZeneca) vaccine was needed to provide long-term protection.

    Refer to COVID-19 vaccination- ATAGI clinical guidance on COVID-19 vaccine in Australia in 2021 for more information.

  • How much protection do I get from 1 dose of Vaxzevria (AstraZeneca)?

    The level of protection gained from a single dose of Vaxzevria (AstraZeneca) was assessed during clinical trials in an exploratory analysis that included participants who had received one dose. Protection was 73%, with the 95% CI from 49% and 86%, starting from 3 weeks after the first dose. This analysis reflects the short term efficacy and does not demonstrate the duration of protection. It is important to note that Vaxzevria is provisionally licensed by the Therapeutic Goods Administration as a two dose schedule.

    Refer to COVID-19 vaccination- ATAGI clinical guidance on COVID-19 vaccine in Australia in 2021 or COVID-19 AstraZeneca Product Information for more information.

  • ATAGI have noted that “people of any age without contraindications who have had their first dose of Vaxzevria (AstraZeneca) without any serious adverse events should receive a second dose of the same vaccine``. What constitutes a serious adverse event?

    A serious adverse event following immunisation (AEFI) includes anaphylaxis or thrombosis with thrombocytopenia syndrome (TTS).

    Anaphylaxis to a previous dose of a vaccine is a contraindication to future doses of that same vaccine.

    As a precaution those with a past history of TTS, cerebral venous sinus thrombosis (CVST), heparin-induced thrombocytopenia (HIT), idiopathic splanchnic (mesenteric, portal and splenic) venous thrombosis, anti-phospholipid syndrome (with thrombosis and/or miscarriage), or capillary leak syndrome are advised not to receive Vaxzevria (AstraZeneca).

    All adverse events should be reported to SAEFVIC. Specialist immunisation advice can be sought by referring patients to the VicSIS.

  • I have a history of capillary leak syndrome, can I have the Vaxzevria (AstraZeneca)?

    An extremely rare relapsing-remitting condition known as capillary leak syndrome has been reported overseas following vaccination with Vaxzevria (AstraZeneca). The syndrome results in fluid leaking from capillaries (small blood vessels) into surrounding tissue and can lead to severe organ damage or death if left untreated.

    In two of the reported cases there was a previous history of capillary leak syndrome. As triggers for relapse are not well understood, the manufacturer of Vaxzevria has updated the product information advising it is not recommended that the vaccine be administered to people with a history of capillary leak syndrome. Individuals with a history of capillary leak syndrome should be referred to their closest VicSIS clinic for further assessment.

    Further information can be found at TGA: COVID-19 weekly safety report.

  • I am over 60 years of age and my GP has recommended that I be immunised with Comirnaty (Pfizer) or Spikevax (Moderna). What happens now?

    Due to increases in vaccine supply to Australia from October 2021, any restrictions on access to COVID-19 vaccine brands has been removed. Comirnaty (Pfizer) and Spikevax (Moderna) are now available to those 60 years and over.

    Individuals who have received their first dose of a COVID-19 vaccine without any serious side effects are recommended to complete the course with the same brand. Combined or mixed COVID-19 vaccine schedules are not routinely recommended in Australia.

Authors: Daniela Say (MVEC Immunisation Fellow), Georgina Lewis (SAEFVIC Clinical Manager, Murdoch Children’s Research Institute), Rachael McGuire (MVEC Education Nurse Coordinator) and Francesca Machingaifa (MVEC Education Nurse Coordinator)

Reviewed by: Rachael McGuire (MVEC Education Nurse Coordinator) and Francesca Machingaifa (MVEC Education Nurse Coordinator)

Date: November 16, 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.