On December 24, 2021, Dr Noelyn Hung wrote in the NZ Herald about her sadness as the pathologist investigating the sudden death of a 26-year-old man of myocarditis, a rare inflammatory condition of the heart, 12 days after receiving the first dose of the Pfizer Covid-19 vaccine.
A review by the Independent Covid-19 Vaccine Safety Monitoring Board agreed that vaccine-related myocarditis had caused his death. Hung went on to calculate that if all 5 million people in New Zealand were infected with SARS-CoV-2 (the virus causing Covid-19) that 2,500 people would die of myocarditis compared with 20 deaths from myocarditis if all 5 million received Pfizer vaccine.
• This opinion has been written in response to a column by Amanda Vickers.
Amanda Vickers disputes these calculations, concluding that – in the specific case of young males – the risks of myocarditis from the Pfizer vaccine are about the same as from Covid-19. So, which numbers are right and more importantly how do the risks and benefits of Pfizer vaccine stack up for young men?
Important though myocarditis is, to get an overall view of the risks of Covid-19 and the benefits and risk of Covid-19 vaccines, it is important to look at the risk of severe disease across the board.
Let's start with deaths – how many could we expect without Covid-19 vaccination and do they vary with age?
It is important, as Vickers says, to be clear about how the chances of dying are being calculated – are we interested in the risk of dying from any infection with the SARS-CoV-2 virus (the infection fatality rate) or the figure Hung used – the percentage of diagnosed cases of Covid-19 who die (the case fatality rate)?
Hung used an overall case fatality rate of 2 per cent to calculate that, assuming everyone in New Zealand would eventually get Covid-19, without vaccine 100,000 people would die.
Vickers' calculations are closer to the mark because, even if all 5 million people in New Zealand had SARS-CoV-2 infection, the proportion who develop symptoms, and especially who become severely ill and require hospital care, goes up very steeply with age, so the 2 per cent figure is far too low for older adults and far too high for the young.
In fact, in New Zealand to date there is such intensive testing (the highest number of tests per identified infection in the world according to Our World in Data) that it is not necessary to also use antibody tests to find undiagnosed infections – we are likely to know about them all.
The situation was similar during the delta outbreak in New South Wales (until omicron hit) – huge amounts of testing, with and without symptoms, so you could be confident that close to all infections were identified.
Between June and October 2021, out of 13,591 positive PCR tests in people 20 to 29 years, 84 needed ICU care (0.61 per cent or 1 in 164) and 6 died (0.044 per cent or 1 in 2265) – about five times higher than quoted by Vickers (0.009 per cent).
For a more complete picture on vaccine safety, probably the best information comes from a study in Israel, which like New Zealand uses only the Pfizer vaccine.
This study used data for everyone enrolled in a large health insurance organisation (covering everything from testing to hospital care for its almost 5 million members) to match almost 900,000 people who had received Pfizer vaccine (most two doses) with 900,000 who hadn't and also 170,000 people Covid positive ( by PCR) with 170,000 tested but negative.
Across this whole population, a range of heart problems like arrhythmia (irregular heart beat) and myocardial infarct (heart attack) were more common than myocarditis as were clots in the lungs or the legs – the only problems where the difference between vaccinated and unvaccinated was higher than expected were myocarditis, lymphadenopathy (inflamed lymph nodes) and herpes zoster (shingles), but there were three extra cases of myocarditis per 100,000 people vaccinated compared with 11 extra per 100,000 people infected.
What about myocarditis? In another study, a closer look was taken at the same health insurance organisation in Israel.
From about 2.6 million people who had received one or two doses of Pfizer vaccine, 54 definite cases of myocarditis were identified, of which 37 (69 per cent) occurred after dose 2, most (41; 76 per cent) were mild and 31 were in 20- to 29-year-old males (11 per 100,000 or 1 in 9350). One case was very severe (would have died but for heart-lung bypass).
This is about a 1 in 300,000 chance of a dying from vaccine-associated myocarditis in this age group, which has to be seen in the light of the more than a hundred times greater risk of dying from Covid-19 for 20–29-year-olds in NSW delta outbreak (1 in 2265).
It is a risk worth accepting only because Covid-19 in the unvaccinated can be severe, even in the young, and the vaccine so effective (in this age group 100 per cent against severe disease).
Vickers also refers to a large English study of myocarditis after Covid-19 vaccines or Covid disease (PCR positive) which included 20 million first doses of Pfizer vaccine, 17 million second doses and almost 11 million booster doses.
With these large numbers, the authors estimated that for every million doses given to males less than 40 years there were three extra myocarditis cases after first doses, increasing to 12 after second doses and about the same (13) after booster doses compared with 7 per 100,000 males in this age group who had tested positive by PCR.
This looks like a big difference but, because myocarditis is so rare from a statistical point of view, the real numbers for vaccine and infection-related myocarditis could lie in a similar range (somewhere between 7 and 15 per 100,000 for booster doses versus between 2 and 11 for Covid disease).
As Vickers points out, in this study the risk of myocarditis from Covid was a lot higher and the risk of post Pfizer vaccine myocarditis a lot lower in both men and women over 40 years and in women under 40 there was no more myocarditis after vaccine than would be expected by chance.
In summary, while the myocarditis numbers in the "demographic" Vickers refers to (20- to 29-year-old males) may look scary at first sight, especially in the light of the tragic death discussed by Hung, it is important to look at the bigger picture.
For myocarditis post vaccine, the risk of a severe episode such as the tragic death which occurred is more than a hundred times lower than the risk of death in unvaccinated people in this age group.
Importantly, as highlighted by the Independent Covid-19 Vaccine Safety Monitoring Board, clear instructions for what to look out for and not hesitating to seek advice if concerned are vital.
Overall and in all age groups, the benefits of vaccination for protection against severe disease continue to make this a no-brainer. Continued close monitoring of risk benefit remains important.
• Peter McIntyre is a professor at Dunedin School of Medicine, University of Otago; medical advisor to the Immunisation Advisory Centre and Honorary Professor with University of Auckland.
• Nikki Turner is medical director at the Immunisation Advisory Centre and Honorary Professor, University of Auckland