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Adolescents at most risk of developing myocarditis: TGA

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The Therapeutic Goods Administration (TGA) has released the latest data on vaccine safety in Australia, which for the first time includes reporting on the newly available Moderna mRNA vaccine.
 
The latest COVID-19 vaccine weekly safety report analyses reported adverse reactions related to the approximately 26.8 million vaccine doses administered in Australia up to 26 September, including 16.1 million first doses and 10.7 million second doses.
 
New data from AusVaxSafety has also shown that adolescents aged 12–19 are reporting similar short-term vaccine side effects to those reported by older Australians.
 
The government-funded national vaccine safety system has so far received more than 150,000 completed day-three safety surveys from adolescents aged 12–19, and the data analysis has not detected any safety signals for this age group.
 
AstraZeneca
An additional seven reports of blood clots and low blood platelets have been assessed as confirmed or probable thrombosis with thrombocytopaenia syndrome (TTS) in the past week, bringing the total number of cases to 148 (83 confirmed, 65 probable).
 
Four of the newly confirmed TTS cases were in individuals aged under 60, including a 19-year-old woman from Victoria.
 
Three of these new cases have been discharged from hospital, but one person remains critically unwell in intensive care. A further 10 people remain in hospital with TTS.
 
In Australia, the risk of dying from TTS after vaccination is approximately one in a million for people receiving a first dose, with that likelihood decreasing when both doses are taken into consideration.
 
To date, 16 cases of TTS have occurred after the second dose. All of these were in people older than 50, with 13 in people over 60. Only three cases were classified as the more serious Tier 1, which involve clots in an unusual location and tend to have more serious outcomes.
 
The TGA assessed adverse reports related to approximately 11.6 million doses of AstraZeneca that had been administered in Australia to 26 September.
 
Pfizer
The TGA has received 115 reports classified as likely to be myocarditis from approximately 15.1 million Pfizer doses administered in Australia. A further 42 reports could not be classified because they did not contain enough information.
 
For the first time, Australia’s health regulator has released domestic rates of myocarditis in relation Pfizer, which confirm it is more likely to occur after the second dose.
 
The condition is estimated to be occurring at a rate of:

• 0.7 cases per 100,000 first doses
• 1 case per 100,000 second doses
• 1.4 cases per 100,000 first doses in recipients aged 12–19
• 4.7 cases per 100,000 second doses in recipients aged 12–19.

However, while the 12–19 cohort reported the highest rates in Australia, the youngest local case classified as ‘likely myocarditis’ to date was 16 years old.
 
Most of the patients with myocarditis experienced symptoms within three days of vaccination. Just over half required treatment in hospital, but most were discharged within four days.
 
Moderna
Approximately 36,000 doses of Moderna had been administered to 26 September. The TGA has received five reports of suspected adverse events related to these doses.
 
All of the adverse reactions recorded so far are consistent with what has been reported in the trials and included injection-site reactions, fever, dizziness and fainting.
 
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AstraZeneca Moderna myocarditis Pfizer TGA TTS vaccine safety

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