Do COVID-19 vaccines cause myocarditis in younger men at a rate higher than the virus?

Question

Dr Keith Moran is a practising physician and consultant in internal medicine with a Youtube Channel discussing medicine.

In May 2023, he posted a video talking about the risks of myocarditis (inflammation of the heart muscle) from COVID-19 vaccinations in comparison with the corresponding risk of myocarditis from catching COVID-19.

He explains

Myocarditis from the vaccine do, of course, vary based on age, sex, second dose being higher, and they're much more common with Moderna.

He goes on to make the claim, at 2m21s:

You still see people (physicians included, in fact) claiming that myocarditis is more common from COVID-19 than it is from vaccination, and that's clearly - in the young male age group below 40 - not true. It's far more common after vaccination in that age group than with infection and numerous studies have suggested that this is on the order of 20 to 50 times greater.

Given the vaccines give expose the body to safe versions of parts of the virus, it makes no sense to me that exposure to a vaccine could cause more myocarditis than exposure to the virus.

[Moran later discusses the difference between clinical and subclinical myocarditis. It isn't clear if his claim is about clinical myocarditis, or both.]

Is Moran correct in his claim?

Answer 1

This is probably a (biased) extract from a study like this (Hippisley-Cox et al.), that did look at age groups specifically:

Subgroup analyses by age showed that the increased risk of events associated with the two mRNA vaccines was present only in those aged under 40  years. For this age group, we estimated 2 (95% CI 1, 3) and 8 (95%CI 4, 9) excess cases of myocarditis per 1  million people receiving a first dose of BNT162b2 and mRNA-1273, respectively, and 3 (95% CI 2, 4) and 15 (95%CI 12, 16) excess cases of myocarditis per 1  million people receiving a second dose of BNT162b2 and mRNA-1273, respectively. This compares with ten (95% CI 7, 11) extra cases of myocarditis following a SARS-CoV-2 positive test in those aged under 40 years.

So yeah, one the two mRNA vaccines (Moderna, which had higher dose of the spike) did exhibit slightly higher myocarditis rate on the 2nd dose than actual infection (12-16 vs 7-11) but the other mRNA vaccine (Pfizer) had lower, non-overlapping reports (2-4) even on the 2nd dose. So quite possibly there's dose-dependent response, and the average infection [in that study] released less of the spike than the Moderna vaccine.

(I should say that I found this study in part because the original Q, before it was edited with the actual quote, only mentioned the Moderna vaccine.)

But the Q-quoted claim that "numerous studies have suggested that this is on the order of 20 to 50 times greater" seems far off based on this study.

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As for the other answer, in fact the Danish study separately looked at infections (aside from vaccine vs unvaccinated). And for the former:

In comparative analyses of outcomes within 28 days of a positive SARS-CoV-2 test (tables S17-S19 and fig S5), SARS-CoV-2 infection was associated with an adjusted hazard ratio of 2.09 (95% confidence interval 0.52 to 8.47) for myocarditis or myopericarditis, but our statistical precision was limited."

This is actually higher that what they found for vaccine overall "adjusted hazard ratio 1.34 (95% confidence interval 0.90 to 2.00)", but the intervals are overlapping. Alas the infection results are not broken down by age in that piece due to not enough observations, which also caused the fairly large confidence interval for the infected (even straddling 1). They basically observed 3 people infected (table S18.)

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There are some other studies that similarly found that myocarditis risk was higher after Moderna compared to Pfizer, and that this difference was more pronounced in young males--one study reported "aOR: 5.09; 95% CI: 2.68-9.66" for that age and sex group (Moderna vs. Pfizer). OTOH other studies didn't find such a difference between the two mRNA vaccines. FWTW, there's one study from France that found a RR as high as 44 (95%CI 22-88) for the Moderna vaccine in the under 24 male group, and also as high as 41 (95%CI 12-140) for females in the same age group--the latter finding is a bit at odds with most other studies; their Pfizer numbers for the same groups are 13 (95%CI 9.2-19) and 9.6 (4.3-22) for males and females, respectively. The Moderna vaccine was much less used in France though, so the raw counts that drive these results (which also have a fairly large range) are substantially smaller for Moderna, about 10 times fewer--see their table S2). A US study (Kaiser) that was specifically limited to those under 39 y.o. also found a difference between the two vaccines, but considerably smaller "In head-to-head comparisons 0–7 days after either dose, risk was moderately higher after mRNA-1273 than after BNT162b2 (RR: 1.61, CI 1.02–2.54)."

But most of these studies (including the one from France) generally don't have an (naturally) infected arm, so they're not that useful for the Q at hand here.

Also, risks (for either vaccine) don't seem to increase on a 3rd/booster dose those; that result has been replicated separately in another study that only looked at the Pfizer booster.

Answer 2

Review of materials Does not support this claim, but is vague on the specific age-group.

Ref: Voleti N et al Myocarditis in SARS-CoV-2 infection vs. COVID-19 vaccination: A systematic review and meta-analysis. Front Cardiovasc Med. 2022 Aug 29;9:951314. doi: 10.3389/fcvm.2022.951314. PMID: 36105535; PMCID: PMC9467278.

We found that the risk of myocarditis increased by a factor of 2 and 15 after vaccination and infection, respectively. This translates into more than a 7-fold higher risk in the infection group compared to the vaccination group. Among the persons with myocarditis in the vaccinated group, 61% (IQR: 39–87%) were men. Younger populations demonstrated an increased risk of myocarditis after receiving the COVID-19 vaccination. Nevertheless, the risk of hospitalization and death was low.

Danish population level study supports this claim

ref: Husby A, et al. SARS-CoV-2 vaccination and myocarditis or myopericarditis: population based cohort study. BMJ. 2021 Dec 16;375:e068665. doi: 10.1136/bmj-2021-068665. PMID: 34916207; PMCID: PMC8683843.

During follow-up, 269 participants developed myocarditis or myopericarditis, of whom 108 (40%) were 12-39 years old and 196 (73%) were male. Of 3 482 295 individuals vaccinated with BNT162b2 (Pfizer-BioNTech), 48 developed myocarditis or myopericarditis within 28 days from the vaccination date compared with unvaccinated individuals (adjusted hazard ratio 1.34 (95% confidence interval 0.90 to 2.00); absolute rate 1.4 per 100 000 vaccinated individuals within 28 days of vaccination (95% confidence interval 1.0 to 1.8)). Adjusted hazard ratios among female participants only and male participants only were 3.73 (1.82 to 7.65) and 0.82 (0.50 to 1.34), respectively, with corresponding absolute rates of 1.3 (0.8 to 1.9) and 1.5 (1.0 to 2.2) per 100 000 vaccinated individuals within 28 days of vaccination, respectively. The adjusted hazard ratio among 12-39 year olds was 1.48 (0.74 to 2.98) and the absolute rate was 1.6 (1.0 to 2.6) per 100 000 vaccinated individuals within 28 days of vaccination. Among 498 814 individuals vaccinated with mRNA-1273 (Moderna), 21 developed myocarditis or myopericarditis within 28 days from vaccination date (adjusted hazard ratio 3.92 (2.30 to 6.68); absolute rate 4.2 per 100 000 vaccinated individuals within 28 days of vaccination (2.6 to 6.4)). Adjusted hazard ratios among women only and men only were 6.33 (2.11 to 18.96) and 3.22 (1.75 to 5.93), respectively, with corresponding absolute rates of 2.0 (0.7 to 4.8) and 6.3 (3.6 to 10.2) per 100 000 vaccinated individuals within 28 days of vaccination, respectively. The adjusted hazard ratio among 12-39 year olds was 5.24 (2.47 to 11.12) and the absolute rate was 5.7 (3.3 to 9.3) per 100 000 vaccinated individuals within 28 days of vaccination.

Wikipedia page, hazard ratio means:

A measure of how often a particular event happens in one group compared to how often it happens in another group, over time.

I'd interpret this as rates of myocarditis in adolescence within 28 days of vaccination with male hazard being higher than female.
BNT162b2 (Pfizer-BioNTech): adjusted hazard ratio 1.34,
mRNA-1273 (Moderna): adjusted hazard ratio 3.92

In results they the paper writes:

Among individuals aged 12-39 years, we also found a significantly increased rate of myocarditis or myopericarditis compared with unvaccinated follow-up (5.24, 2.47 to 11.12).

I'll try to read more publications relating to this as time allows.