Is myocarditis risk worse after vaccination or infection or both?

Clarifying the real-life picture

The official narrative claims that vaccines prevent infection and therefore reduce risk of myocarditis from infection. This claim is reliant on two points:

  1. Vaccines reducing infections
  2. That infection related myocarditis occurs at a lower rate in the vaccinated

What evidence are these claims based on?

There is no shortage of groups with access to large scale health data enabling them to provide a myocarditis incidence rate for the following situations:

  1. Pre-covid background
  2. Uninfected unvaccinated
  3. Infected unvaccinated
  4. Uninfected vaccinated
  5. Infected vaccinated

Instead of providing this data these groups have fudged the answer in various ways. Some have avoided the question of incidence in the unvaccinated; ignored the vaccination status of those infected or even modelled the data in the vaccinated infected and not released the raw data.

A single study using data from forty US hospitals, has addressed the question of how myocarditis incidence has changed over time. They showed that the rise in myocarditis did not begin until spring 2021.

By collating all the available studies we can assess the incidence rate for each of the situations described above. The table shows the incidence for the different groups in the order the papers were published. Where no distinction was made regarding vaccination status or infection status the cells have been merged. To allow fair comparison, where follow up was for more than a month, the numbers have been adjusted to a 28 day window.

DateBackground rateUninfectedUnvaccinatedInfected UnvaccinatedInfected vaccinatedUninfected vaccinatedReference and comments
Jan 2021Not mentionedNot mentionedBackground risk onlyNot mentionedNot mentionedReview of case reports
Jun 20212 in young malesNot mentionedNot mentionedNot mentioned67 in young malesFDA slides – for 7 day window after 2nd dose
Jun 2021Not mentionedNot mentionedNot mentionedNot mentioned160 in young malesIsrael – no time frame
Jul 2021Not mentionedNot mentioned450 in young malesNot mentionedNot mentionedUS – did not know how many infected and had to guess denominator and counted for up to 82 days after infection
Nov 20218.7Not mentionedNot mentionedNot mentioned337 in young malesHong Kong – active 14 day follow up after vaccination 
Nov 2021Not mentionedNot mentioned50,000Not mentionedPfizer sponsored study – no claim to have correct denominator
Dec 2021Not mentionedNot mentionedNot mentioned40 in <40 yr olds5 to 23 in <40 yr oldsOxford – estimate of excess in 28 days
Jan 2022Not mentionedNot mentionedNot mentionedNot mentioned106 in young malesUSA in 7 day window
Jan 2022Not mentionedNot mentionedNot mentionedNot mentioned70 in young malesCDC slide 13 –  7 day window
Feb 20222 in young malesNot mentionedNot mentionedNot mentioned162 in young malesUS data7 day window
Feb 202270Not mentioned380580Not mentionedUS Veterans – Ignored first 30 days – numbers calculated for annual risk here
Apr 2022Not mentioned8 to 10 in young malesRemoved from studyRemoved from study40-280 in young males4 Nordic countries
Apr 2022Not mentionedNot mentionedNot mentionedNot mentioned100 Pfizer consent form
Apr 2022Not mentioned88Not mentionedNot mentionedIsraeli – based on maximum follow up of 6 months
May 2022Not mentionedNot mentionedNot mentionedNot mentioned198 in young malesPublic health Ontario
Jun 20225Not mentioned1500 – (unreferenced)Up to 69 in young malesMHRA estimates
Risk per million infections / doses over differing time periods depending on the study (see comments)

The Pfizer sponsored study is a clear outlier with a claim of 5% of covid infected patients having myocarditis. The paper did not claim to have a reliable denominator as it was based on healthcare records and therefore biassed towards patients who needed medical attention. This figure and the unreferenced MHRA claim are in no way consistent with the change in incidence over time nor with the other studies.

The background rate is up to 8 per million per 28 days. The rate in the uninfected unvaccinated was similar. The unvaccinated infected rate was calculated separately on three occasions with measures ranging from background rates to 31 per million per 28 days. The figure of 450 per million was based on a modelled denominator. The follow up was for up to 82 days but the distribution in that time did not appear to be constant making it difficult to interpret. 

The myocarditis rates in the infected vaccinated population ranged from 40 to 280 based on three separate studies. This is between 5 and 35 times higher than the background rate and 9 and 35 times greater than in the infected unvaccinated. The rates for uninfected vaccinated young men overlaps with the rates after infection in the vaccinated but includes estimates that are higher. The rate from the Hong Kong study of 337 per million is particularly notable as this was measured by actively following up those vaccinated rather than measuring passively or only capturing those that presented to hospital later.

The evidence that infection presents an increased risk of myocarditis in the unvaccinated is conflicting but even those studies that claim an increased risk in this group show it is lower than for the infected vaccinated. Vaccination itself presents a significant risk, especially in young males and the risk after infection in the vaccinated is higher than in the unvaccinated.

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