Following investigations nationally and internationally into a rare blood clotting condition known as Thrombosis with Thrombocytopenia Syndrome (TTS) occurring in people who have received COVID-19 AstraZeneca, ATAGI have provided updated advice for the administration of COVID-19 vaccines in Australia.

ATAGI recommends that Comirnaty™ is the preferred brand for immunisation of those under 50 years of age who have not already received dose 1 of COVID-19 AstraZeneca, with COVID-19 AstraZeneca available for immunisation of those over 50 years of age. Individuals who have had their first dose of COVID-19 AstraZeneca without any serious adverse events can proceed with the second dose. COVID-19 AstraZeneca can continue to be used in adults aged under 50 years where the benefits are likely to outweigh the risks for an individual (an informed decision can be made following a discussion on the risks and benefits).

TTS is a newly described serious condition, which presents with unusual blood clots (thrombosis) in the brain or other parts of the body, accompanied by a low number of platelets (thrombocytopenia). It has been noted to develop 4-20 days following vaccination with COVID-19 AstraZeneca. Global reports show TTS may occur in approximately 4-6 people per million doses delivered, with 1 case recorded in Australia to date. It is noted to predominantly occur in younger adults however there have been some cases reported in older vaccine recipients. So far there has been no pre-existing conditions or biological factors identified that may predispose or decrease the risk of someone developing TTS.  The exact mechanism leading to this condition is not fully understood however antibodies (anti-PF4 antibodies) that activate platelets have been detected in some people who have developed TTS. These antibodies have also been detected in people with similar symptoms following administration of the drug heparin (heparin induced thrombocytopenia).

ATAGI has made this recommendation after considering the current level of community transmission of COVID-19 disease in Australia, as well as the likely severity of disease according to age if exposed to COVID-19. Should the level of risk change or more information becomes available these recommendations may change. ATAGI continues to recommend all adults be vaccinated against COVID-19 as the virus continues to cause severe disease globally.

To read the advice in full refer to:

ATAGI statement on AstraZeneca vaccine in response to new vaccine safety concerns