Like other countries, we have observed a higher-than-expected number of cases of myocarditis in vaccinated compared to unvaccinated individuals for Comirnaty (Pfizer). The Global Advisory Committee on Vaccine Safety at the World Health Organization has recently stated that current evidence suggests a likely causal association between myocarditis and the mRNA vaccines.

In some countries, higher rates of myocarditis and pericarditis have been reported with Spikevax (Moderna) than with Comirnaty (Pfizer). Because the number of cases of myocarditis reported after Spikevax (Moderna) in Australia is small, we are not yet able to calculate reliable reporting rates for it or to see any difference in risk between the 2 vaccines. The current overall estimated rates (for the entire population) of myocarditis for Comirnaty (Pfizer) and Spikevax (Moderna) are similar (1.4 cases per 100,000 Comirnaty doses versus 1.8 cases per 100,000 Spikevax doses). However, statistical analysis shows that there is more uncertainty around the reporting rate for Spikevax (likely to be between 1.2 and 2.5 cases per 100,000 doses) than for Comirnaty (likely to be between 1.3 and 1.6 cases per 100,000 doses).

Reports received by the TGA of suspected myocarditis and pericarditis for the mRNA vaccines are provided in Table 1. We have reviewed these reports against an internationally accepted criteria to classify the likelihood of myocarditis. This assessment does not determine whether cases have been caused by vaccination.

*Cases reporting both myocarditis and pericarditis are included in suspected myocarditis cases

‡ Cases classified as level 1 are confirmed to be myocarditis based on strong clinical evidence including the patient’s symptoms, and results of tests and imaging indicating a diagnosis of myocarditis. Level 2 cases are probably myocarditis based on a combination of symptoms and routine tests for heart conditions. Level 3 cases are possibly myocarditis based on symptoms and a doctor’s report that myocarditis is the most likely diagnosis in the absence of medical tests and investigations. For all cases of suspected myocarditis, where possible, other known causes of the patient’s symptoms or test results are ruled out before cases are classified.

†The youngest case classified as ‘likely myocarditis’ to date was 12 years old.

¥The number of suspected pericarditis cases for Comirnaty (Pfizer) has decreased since last week as cases containing both myocarditis and pericarditis were inadvertently included in last weeks’ report, and some cases have been identified as duplicates and removed.

As we have received limited adverse event reports for Spikevax (Moderna), our analysis of likely myocarditis cases by age and dose focuses on data for the Comirnaty (Pfizer) vaccine (see Table 2). The estimated reporting rates in Australia appear similar to overseas rates.

*The rate includes cases of myocarditis that occurred after vaccination but may not be vaccine related. The number of younger people vaccinated is still relatively low in Australia, so estimated reporting rates are based on limited data.

We continue to monitor and review Australian data on myocarditis and will provide regular updates in this report as more information becomes available. We are also working closely with international medicines regulators to share emerging safety information.

For more information, see guidance on myocarditis and pericarditis developed by ATAGI and the Cardiac Society of Australia and New Zealand (CSANZ).

From about 13.5 million vaccine doses, there have been 166 cases of TTS. Of these, 144 (82 confirmed, 62 probable) related to a first dose of Vaxzevria (AstraZeneca) and 22 to a second dose (6 confirmed, 16 probable). This includes 2 new cases of TTS reported this week (see Table 3).

‡As previously reported, the TGA determines whether a report is likely to represent TTS by assessing cases against accepted criteria established by the UK’s Medicines and Healthcare products Regulatory Agency. Cases may be reclassified as further information becomes available.

When assessed against the criteria used by the US Centers for Disease Control and Prevention (CDC), approximately one-third of the cases reported to the TGA after a first dose are classified as Tier 1 (Table 4). These cases tend to have more serious outcomes involving clots in unusual locations, such as the brain or abdomen. Women in younger age groups seem to be slightly more likely to develop these kinds of clots. Australian data indicates that patients aged under 50 years are more likely to be classified as Tier 1 and/or require treatment in intensive care.

Cases reported after a second vaccine dose are much less likely to be classified as Tier 1 with most people having clots in common locations, such as the lungs or legs. The majority of these cases occurred in people over the age of 60 years old.

‡ Rates of TTS are calculated as of 4 November 2021 to account for the time to onset of TTS. These rates are estimates of risk based on small numbers of cases so far. Aggregated rates are given for some age ranges where the number of cases for a 10-year age bracket is too low to calculate reliable estimates.

† The US CDC classification of Tier 1 is defined as clots in an unusual location (such as the brain or abdomen) and a low platelet count with or without antibodies that activate platelets (anti-PF4 antibodies).

Cases of TTS have most often occurred about 2 weeks after vaccination, although the time to onset or diagnosis varies (Table 5). Eight people have died as a result of TTS – 6 of these were women. In Australia, the risk of dying from TTS after vaccination is about one in a million (people receiving a first dose), and somewhat less than this when both doses are taken into consideration.

*Data is based on the most recent medical information available to the TGA for first and second dose TTS cases.
†As previously reported, one patient died from unrelated medical conditions while being treated for TTS. The outcome for this patient is not included in this table.