Vaccination remains the best way to protect against severe illness and death from COVID-19 and is a core element of the pandemic response.
ATAGI is continuing to monitor local and international data on a rare and new condition that occurs after AstraZeneca COVID-19 vaccine called thrombosis with thrombocytopenia syndrome (TTS).
ATAGI has reviewed the additional 3 cases of TTS confirmed by the TGA on 22 April 2021 in Australia, bringing the total confirmed cases to six. Of these cases, 5 people were under 50 years of age. All had received their first dose of AstraZeneca COVID-19 vaccine between 4 and 26 days before the onset of symptoms.
Cases have varied in severity but included one fatal case. People who have had TTS can make a full recovery, although some may have ongoing organ damage, including to the brain (similar to stroke) and to abdominal organs, that can result in long term health impacts.
These TTS cases have occurred amongst approximately 730,000 individuals administered an AstraZeneca COVID-19 vaccine prior to the 11th April 2020. ATAGI estimates that the overall rate of TTS is about 6 cases per million people vaccinated, but the rate is currently estimated to be higher (20-40 cases per million) in those under 50 years of age. However, Australian-estimated age-specific incidence rates are imprecise due to small numbers and will be updated as further information become available.
ATAGI have made previous recommendations on this issue, most recently on 8 April.
ATAGI reinforces its previous advice that:
- Comirnaty (Pfizer) is preferred over AstraZeneca COVID-19 vaccine in people under the age of 50 years. The AstraZeneca COVID-19 vaccine can still be given to adults under 50 years if Comirnaty is not available, if the benefit of vaccination is likely to outweigh risk, and where informed consent has been obtained.
- In people aged 50 years and over, the benefits of AstraZeneca COVID-19 vaccine outweigh the risks associated with vaccination. This is due to the ongoing potential for COVID-19 outbreaks, the widespread susceptibility of the Australian population, and the strong relationship of severe COVID-19 and mortality with increasing age.
- Overseas, cases of TTS have occurred in people of all ages, but the risk of TTS appears to be lower in those 50 years and over than in younger adults. The TGA and ATAGI are continuing to monitor the rates of cases in this age group and will advise as more data becomes available.
People who are considering vaccination with AstraZeneca COVID-19 vaccine should be aware of this potential complication as part of providing informed consent. Those who choose to delay vaccination until a vaccine other than AstraZeneca COVID-19 vaccine is available should be aware that they may not be protected against COVID-19 for many months. ATAGI acknowledges the challenges of decision making as information continues to emerge.
ATAGI continues to recommend that people who have received a first dose of AstraZeneca COVID-19 vaccine without serious adverse events can be given a second dose. Current data suggest that the risk of TTS following a second dose is considerably lower than with a first dose (with one case reported from more than 2 million second doses given in the UK to 14 April 2021), and there are no studies of the effectiveness of mixed schedules of different vaccine types. ATAGI will continue to review evidence on this issue.
Background
ATAGI notes that a total of 168 cases of thrombosis with thrombocytopenia following AstraZeneca vaccine have been reported in the UK as of 14th April 2021, out of a total of 21.2 million first doses and 2.3 million second doses given. Additional cases have been reported in Europe but total case numbers are not clear.
The assessment and advice provided by ATAGI is specific to the context of no current but potential future community transmission of COVID-19 and will need to be reviewed should circumstances change. Other considerations were noted in ATAGI’s previous statement on 8 April.
ATAGI notes the potential for incursion of COVID-19 in the Australian community remains high with the worsening global situation, including in many countries in our region. The risk-benefit assessment and advice will be different in situations with higher community incidence of COVID-19.
Resources for providers and consumers will be updated in the coming days.
Definitions
- Thrombosis with thrombocytopenia syndrome (TTS) is a rare and new syndrome which has been reported after being given the AstraZeneca COVID-19 vaccine. It may be caused by this vaccine. The condition involves blood clots (occurring in body sites like the brain or abdomen) together with low platelet levels.
- Thrombosis is the formation of a blood clot, which prevents blood flowing normally through the body. While thrombosis is usually a normal response to prevent bleeding (e.g. following injury), in this case this process is abnormal.
- Thrombocytopenia is a condition in which you have a low blood platelet count. Platelets (thrombocytes) are blood cells that help blood clot. Platelets stop bleeding by clumping and forming plugs in blood vessel injuries.
