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Doubts over study linking mRNA vaccines and adolescents’ myocarditis risk
A study co-author has been connected to an online group opposing pandemic public health measures, from mask-wearing and lockdowns to mandatory vaccinations.
The TGA has recorded 12 cases of suspected myocarditis/pericarditis in children aged aged 15–17. (Image: AAP)
The pre-print study, uploaded to the medRxiv server on 8 September, suggests boys aged 12–17 without medical comorbidities are more likely to develop a cardiac adverse event (CAE) that requires hospitalisation following vaccination with either Pfizer or Moderna than they are to be hospitalised with COVID-19.
The research, led by Dr Tracy Høeg from the University of California, used the Vaccine Adverse Event Reporting System (VAERS) to identify 257 CAEs among vaccinated adolescents between 1 January and 18 June.
It found rates of CAE were 16.2 per 100,000 for 12–15-year-old boys and 9.4 per 100,000 for 16–17-year-olds. The rates for girls were significantly lower, at 1.3 per 100,000 and 1.34 per 100,000, respectively.
The authors concluded that the rate of CAE for healthy boys aged 12–15 is 3.7–6.1 times higher than their risk of being hospitalised for COVID-19, and 2.1–3.5 times higher for boys aged 16–17.
However, doubt has been cast over the study as news has emerged that a co-author, Josh Stevenson, is associated with Rational Ground, an online group that has opposed public health measures, including mandatory vaccinations, throughout the pandemic.
Questions have also been raised over the study’s use of data from the VAERS platform, which relies on unverified self-reports of side effects that have reportedly been used by the anti-vaccination movement to spread misinformation.
This revelation has given way to concerns that the study could be causing unnecessary anxiety among parents and carers, as Australia and the UK have now included 12–15-year-olds in their COVID vaccination programs.
Professor Robert Booy, an infectious diseases paediatrician and vaccine expert, urged caution in interpreting the study. While there is considerable evidence that myocarditis is a
real, albeit rare, side effect of the mRNA vaccines, he said the true risk estimate is likely to be more conservative.
‘The truth of the data probably rests more at a risk of between one in 15,000–20,000 [5–6.66 per 100,000],’ Professor Booy told
newsGP. ‘And, fortunately, it is rarely leading to serious consequences or long-term damage.
‘It’s extremely unlikely for a CAE to last longer than 1–2 weeks and a fatal outcome is extremely rare – I think I’ve read one case report.’
It was in July that the Therapeutic Goods Administration (TGA) included a warning statement about myocarditis and pericarditis as rare sides effect of Pfizer, particularly among males under 30.
In its
latest safety report, the regulator said that up to 5 September it had received 370 reports of suspected myocarditis and/or pericarditis following vaccination with Pfizer, including 10 boys and two girls aged 15–17. Five cases occurred after the first dose and seven after the second dose.
The rare side effects typically occur within 10 days of vaccination, particularly after the second dose, and more often in younger men.
However, the TGA notes that ‘myocarditis and pericarditis are much more common with COVID-19 infection and damage to the heart is frequently severe after infection’.
Professor Booy assures that the Australian regulator, along with those in the UK and US, are continually and carefully looking at emerging data, and that the risk–benefit analysis to date remains in favour of vaccination.
While the emergence of the Delta strain has resulted in COVID-19 spreading more easily in schools,
recent Australian research found that most children have only mild disease. And though child deaths from COVID remain rare, with none recorded in Australia to date, Professor Booy says they do – and have – occurred overseas.
‘In the United States, they have 400 children under the age of 18 who’ve died and probably half had a predisposed condition,’ he said.
‘That means half would have been healthy and could only benefit by universal vaccination.’
But Professor Booy said the benefits of vaccination are far-reaching.
‘You’re much better off being vaccinated as a teenager than getting COVID disease, even though it’s relatively mild,’ he said.
‘The added advantage of being able to go back to school, social economic improvements and confidence that people have around COVID prevention and protection lean to multiple reasons for having a preference for vaccinating teenagers.’
With the majority of myocarditis cases occurring after the second dose, the UK has decided to offer 12–15-year-olds
a single dose of either Pfizer or Moderna.
Professor Booy said further investigation is needed to confirm whether reducing the dosage protocol would offer enough protection – and whether it would even reduce the likelihood of myocarditis.
‘Protection against COVID by one dose of vaccination in teenagers is very high, and it would be very worthwhile to do good surveillance in Australia to better understand whether one dose is enough,’ he said.
‘We don’t know whether a lower dose will reduce the likelihood of myocarditis, but it’s a good question.’
Professor Booy did urge caution in paying too much attention to pre-print studies, and said the peer-review process is in place for good reason.
‘It’s an important thing to pay attention to; it is relevant,’ he said. ‘But the harm–benefit still favours vaccination, particularly for a side effect that is only mild to moderate.
‘Parents worried about their athletic teenagers having the vaccine would be wise to keep them away from strenuous exercise for five days after vaccination.
‘But the TGA, the CDC [Centers for Disease Control and Prevention] and MHRA [Medicines and Healthcare products Regulatory Agency] have all looked at it, and they’ve reassured themselves that it’s safe.’
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