AstraZeneca ChAdOx1-S COVID-19 vaccine: no proven link with blood clots
Update - European and UK reviews find no proven link with blood clots
The European Medicines Agency (EMA) and the United Kingdom (UK) Medicines and Healthcare products Regulatory Agency (MHRA) have completed preliminary reviews of the risk of blood clots in people vaccinated with the AstraZeneca COVID-19 vaccine. These reviews have found the benefits of the vaccine continue to outweigh the risks, and the vaccine is not associated with an increase in the overall risk of blood clots.
The TGA attended the EMA's safety committee meeting on 18 March 2021, which found the number of blood clotting cases reported after vaccination, both in the large clinical trials undertaken prior to vaccine authorisation and during rollout of vaccination programs across the world, was lower than that expected in the general population. Around 20 million people in Europe, and several million more in other parts of the world, have received the vaccine.
The EMA safety committee noted there had been a very small number of cases of a rare type of blood clotting disease (disseminated intravascular coagulation) associated with low levels of blood platelets (blood cells that normally help blood to clot), with or without bleeding, as well as extremely rare cases of clots in the vessels draining blood from the brain (cerebral venous sinus thrombosis, CVST). It has not been proven that these cases were caused by the vaccine and a plausible mechanism for how they could have been caused by the vaccine has not been established. These conditions are also sometimes seen in people who have not received a COVID-19 vaccine or other vaccine. The EMA safety committee also noted that COVID-19 disease itself is often associated with serious clotting problems, which can themselves be fatal.
Additionally, the EMA found there was no evidence of a problem related to specific batches of the vaccine or to particular manufacturing sites.
Further details are available in the EMA's press release on the issue.
The MHRA has also published a statement with its own separate review of reported cases and data from hospital admissions and GP records. They found that all the available evidence did not suggest common blood clots in veins were caused by the vaccine. The MHRA is undertaking a detailed review of the five cases of CVST with low blood platelets that occurred in the UK, and also notes that these events can occur naturally.
The MHRA is advising that people in the UK should continue to get the AstraZeneca COVID-19 vaccine when invited to do so.
The relevant expert clinical society, the International Society on Thrombosis and Haemostasis also recommends that all eligible adults continue to receive COVID-19 vaccinations, with the benefits of vaccination strongly outweighing any potential complications even for patients with a history of blood clots or for those taking blood thinning medications.
To 18 March 2021, the TGA has not received any reports of blood clots following administration of the AstraZeneca COVID-19 vaccine in Australia. We advise that people in Australia should continue to get the AstraZeneca vaccine when eligible.
The TGA continues to closely monitor the safety of the AstraZeneca COVID-19 vaccine and will work with AstraZeneca to update Product Information as required. If we detect a safety concern, we will take rapid action to address it and promptly provide information to the public.
16 March 2021
The Therapeutic Goods Administration (TGA) is aware that some additional European countries have paused vaccination with the AstraZeneca ChAdOx1-S COVID-19 vaccine in response to reports of blood clots in vaccinated individuals.
The European Medicines Agency (EMA) continues to investigate the issue and EMA remains of the view that the benefits of the AstraZeneca vaccine in preventing COVID-19, with its associated risk of hospitalisation and death, outweigh the risks of side effects. The EMA's safety (Pharmacovigilance Risk Assessment) committee will meet on Thursday to determine the outcome of its investigation.
The TGA continues to be in close and frequent communication with the EMA regarding its review, and continues to liaise with our international counterparts through the International Coalition of Medicines Regulatory Authorities (ICMRA).
The UK regulator, the MHRA has also released an updated statement: 'It has not been confirmed that the reports of blood clots were caused by the AstraZeneca COVID-19 vaccine. People should still go and get their COVID-19 vaccine when asked to do so'.
To 15 March 2021, the TGA has not received any reports of blood clots following administration of the AstraZeneca COVID-19 vaccine in Australia. AstraZeneca has submitted to the TGA a detailed summary of adverse events reported globally related to blood clots to 8 March, as part of the sponsor's routine safety reporting obligations. The TGA does not have any evidence of a biologically plausible relationship that could suggest a cause and effect relationship between vaccination and blood clots.
Blood clots are considered 'adverse events of special interest', which are closely monitored in Australia and by overseas regulators. The TGA and other regulators conduct analyses to compare the number of reports of these events against the expected rate of events in the population in the absence of vaccination.
Venous thromboembolism (VTE), including deep vein thrombosis (a blood clot in a vein deep below the skin) and pulmonary embolism (a blood clot blocking a blood vessel in the lungs), is the third most common cardiovascular disease globally, with an annual incidence of over 10 million people.
In Australia, at least 17,000 people develop VTE each year. This equates to an average 50 people per day, so unfortunately a significant number of people develop this medical condition. The 2019 Australian guidelines for the diagnosis and management of venous thromboembolism stress that the condition is common, with Australians having an 8% (almost one in 12) risk of developing VTE at some state in their lifetime.
As of this time there is no indication of an increased rate of blood clots happening or cause and effect with the AstraZeneca vaccine in Australia.
Response to overseas precautionary measures
12 March 2021
The Therapeutic Goods Administration (TGA) is aware that some European countries have paused vaccination with the AstraZeneca ChAdOx1-S COVID-19 vaccine after reports of blood clots following vaccination.
The TGA advises that a link between blood clots and the AstraZeneca vaccine has not been confirmed. To 11 March 2021, the TGA has received no reports of blood clots following use of the AstraZeneca ChAdOx1-S vaccine in Australia. Extensive international experience does not indicate an increased risk of blood clots associated with the vaccine. Blood clots can occur naturally and are not uncommon.
Denmark, Iceland and Norway have temporarily ceased vaccination with the AstraZeneca ChAdOx1-S COVID-19 vaccine as a precautionary measure in response to a number of reports of blood clots following administration of the vaccine, including one case in Denmark where a person died. The European Medicines Agency's safety committee is conducting a rapid review of the issue.
Vaccination programs with the AstraZeneca vaccine are continuing in other countries, including the United Kingdom (UK) and France. The UK is encouraging people to continue to be vaccinated.
Blood clots are considered 'adverse events of special interest', which are closely monitored in Australia and by overseas regulators.
The TGA works closely with international regulators and shares information about COVID-19 vaccine safety. If we detect a safety concern, we will take rapid action to address it and provide information to the public.
Consumers and health professionals are encouraged to report problems with medicines or vaccines. Your report will contribute to the TGA's monitoring of these products.
The TGA cannot give advice about an individual's medical condition. You are strongly encouraged to talk with a health professional if you are concerned about a possible adverse event associated with a medicine or vaccine.