Denmark said that, while it was already using the Pfizer vaccine as the main option for people aged 12-17 years, it had decided to pause giving the Moderna vaccine to people below 18 according to a "precautionary principle".
"In the preliminary data ... there is a suspicion of an increased risk of heart inflammation, when vaccinated with Moderna," the Danish Health Authority said in a statement.
It referred to data from a yet unpublished Nordic study, which would now be sent to the European Medicines Agency (EMA) for further assessment. Final data was expected within a month, it added.
In Australia, the Moderna vaccine has been approved for use in people aged 12 years and over.
The Therapeutic Goods Administration on Thursday said it was aware of the Nordic study and it “continues to closely monitor this rare occurrence, including working closely with international medicines regulators to share emerging safety information, and closely monitoring reports in Australia.”
“There has been no change to the approval by the TGA for the Moderna COVID-19 vaccine and it is important to note that at this time the EMA approval of Moderna for people over 12 years of age has also not changed,” a spokesperson told SBS News in a statement.
The TGA said myocarditis and pericarditis are known rare risks associated with the mRNA COVID-19 vaccines, however cases were usually temporary and resolved following treatment and rest.
The regulator said that there had been no confirmed cases of either side effect after about 180,000 doses of the vaccine nationally. There were three suspected - but not yet confirmed - cases of pericarditis associated with the jab.
“These events can occur due to other causes, including common viral infections, so it is expected that not all cases are related to vaccination,” the TGA said.
“In Australia it is estimated that there would normally be one case of myocarditis diagnosed each week in people aged 0-19 years. This can be higher in the winter months when viral infections are more common.”
The benefits of vaccination against COVID-19 far outweigh the risks of very rare adverse events, the TGA added.