We have observed a higher-than-expected number of cases of myocarditis in vaccinated compared to unvaccinated individuals for Comirnaty (Pfizer). This is similar to findings from other drug regulators overseas. 

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. Higher rates of myocarditis and pericarditis have been reported with Spikevax (Moderna) than with Comirnaty (Pfizer) in some countries, including the UK. The TGA is looking closely at Australian reports. However, because use of Spikevax (Moderna) is still relatively low, we are not able to calculate reliable reporting rates for the population. 

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 highly likely to be 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. Other known causes of myocarditis are ruled out before all cases are classified.

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

Of the cases classified as likely to be myocarditis, most of the patients experienced symptoms within 3 days of vaccination. Around half of the patients were admitted to hospital with 8 being treated in intensive care.  Most patients treated in hospital were discharged within 4 days. 

As we have received limited adverse event reports for Spikevax (Moderna), our analysis of likely myocarditis cases 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.

To date, there have been 158 cases of TTS assessed as related to Vaxzevria (AstraZeneca) from about 13.1 million vaccine doses. The risk of TTS after a second dose appears to be much lower than after the first dose. 

Women in younger age groups seem to be slightly more likely to develop clots in unusual locations, such as the brain or abdomen, which have more serious outcomes. 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.

One new case of confirmed TTS was reported this week. This takes the total number of Australian reports assessed as TTS following Vaxzevria (AstraZeneca) to 158 cases (87 confirmed, 71 probable) from approximately 13.1 million vaccine doses.

‡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.

To date, 19 cases of TTS have occurred after the second dose. Thirteen cases have been assessed as probable TTS, with 6 cases assessed as confirmed TTS. All cases have occurred in individuals older than 50 years, with 16 of the cases in people over 60 years of age. The vast majority of the patients had clots in common locations, such as the lungs or legs. Our preliminary analysis is consistent with overseas investigations which have shown that the risk of TTS after the second dose is extremely low (less than one case per 100,000 second doses administered).

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 are classified as Tier 1 cases which tend to have more serious outcomes (Table 4). Tier 1 cases involve clots in an unusual location, such as the brain or abdomen. Australian data indicates that patients aged under 50 years of age are more likely to be classified as Tier 1 and/or require treatment in intensive care.

‡ Rates of TTS are calculated based on first doses of the Vaxzevria (AstraZeneca) vaccine as of 21 October 2021 to account for the time to onset of TTS. These rates are estimates of risk based on small numbers of cases so far. An aggregated rate is given for people aged 18–49 years as the number of cases for each 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 have most often occurred about 2 weeks after vaccination, although the time to onset (or diagnosis) has ranged from 1-83 days (Table 5).

*Data is based on the most recent medical information available to the TGA
†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.