best data i can find is but im having trouble grasping as quite complex
https://www.bmj.com/content/375/bmj-2021-068665
Yeah, they were very thorough, lots of numbers.
The researchers used data from the Danish health system, which means they had very good coverage. However, it means they were only able to track hospitalised cases of myocarditis or pericarditis (but non-hospitalized cases are likely to follow the same pattern). Denmark also used a 5 week interval between the first and second shots while most other countries use 3. Lastly, the number of events is quite low, so the results come with a lot of uncertainty.
External Quote:
Setting Denmark.
Participants 4 931 775 individuals aged 12 years or older, followed from 1 October 2020 to 5 October 2021.
Main outcome measures The primary outcome, myocarditis or myopericarditis, was defined as a combination of a hospital diagnosis of myocarditis or pericarditis.
[...] Finally, we censored individuals with a positive SARS-CoV-2 test result, to avoid associating outcomes of SARS-CoV-2 infection with outcomes of SARS-CoV-2 vaccination.
The study has two different main analyses of this data, with similar results.
• First, they compare people who got vaccinated with people who didn't (cohort study), and adjusted for age, sex, and other differences.
• Secondly, they did a self-controlled case series (SCCS): the idea behind that is that you can get myocarditis at any time, but if the vaccination causes this, people are going to be more likely to have an event right after the vaccination, so you pick everyone with a vaccination and an event and calculate the impact of the vaccination on the timing of the event. The clever thing about this is that everyone is their own control, so you don't need to do any adjustments.
They also looked at other numbers like total incidence and death rates.
External Quote:
Using healthcare data covering the entire Danish population, we did observe a strong association between vaccination with mRNA-1273 and myocarditis or myopericarditis, defined as the combined outcome of a hospital diagnosis of myocarditis or pericarditis, increased troponin levels, and a hospital stay lasting more than 24 hours. Vaccination with BNT162b2 was only associated with an overall increased rate of myocarditis or myopericarditis among female participants. In general, the rate of myocarditis or myopericarditis was about threefold to fourfold higher for mRNA-1273 vaccination than that for BNT162b2 vaccination. Nevertheless, the absolute number of events were low. Even in the youngest age group (12-39 years), the absolute rates of myocarditis or myopericarditis were 1.6 (95% confidence interval 1.0 to 2.6) and 5.7 (3.3 to 9.3) per 100 000 individuals within 28 days of BNT162b2 vaccination and mRNA-1273 vaccination, respectively. Clinical outcomes among vaccinated people with myocarditis or myopericarditis were predominantly mild. We observed no readmissions, diagnoses of heart failure, or deaths among people with myocarditis or myopericarditis occurring within 28 days of mRNA-1273 vaccination.
Overall, this confirms what we already knew: the side effect exists, but it's very rare, and most people who get it don't die.
External Quote:
Fig 1
Hazard ratios of primary and secondary study outcomes within 28 days after vaccination in the cohort study, by vaccine type, with follow-up until 5 October 2021. Hazard ratios are adjusted for age and sex; adjusted hazard ratios are adjusted for age, sex, vaccine priority group, season, and clinical comorbidities
The way this works is that, for each participant, you take the time they spend in each group (just 1 group for the unvaccinated, but vaccinated people switch groups when they get the shot), add it all up, and compare.
For example, for the myocarditis analysis, in the unvaccinated group, there are 155 events and 3.2 million person-years, and among the Biontech vaccinees, we have 0.5 million person-years, so we'd expect 155×(0.5/3.2)≈24 events in that group, but there were 48, so the (unadjusted) risk is doubled.
The table also indicates that vaccinees are less likely to die, which is probably due to "healthy person bias": people on the brink of death don't get vaccinated, which causes more deaths in the unvaccinated group.
The numbers for the SCCS aren't quite the same as for the cohort analysis, but the confidence intervals overlap, which means everything's in the right ballpark:
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One of the extra things they looked at was whether vaccine-induced myocardia is more severe than normal myocardia; it seems there is no noticeable difference:
External Quote:
Vaccination status did not appear to be associated with the clinical outcome of participants who had myocarditis or myopericarditis, although our precision is limited because our cohort had only a few individuals with severe outcomes. Among 155 unvaccinated individuals who had myocarditis or myopericarditis, it was estimated that 47.7% (95% confidence interval 39.7% to 55.3%) were still in hospital 72 hours after admission, 4.5% (2.2% to 9.2%) were diagnosed with heart failure, and 1.9% (0.6% to 5.9%) died within 28 days of the myocarditis or myopericarditis event (table S8). Corresponding rates for the 48 individuals who had myocarditis or myopericarditis within 28 days of BNT162b2 vaccination were 58.3% (43.2% to 70.8%), 2.1% (0.3% to 13.9%), and 2.1% (0.3% to 13.9%), respectively. For the 21 individuals who had myocarditis or myopericarditis within 28 days of mRNA-1273 vaccination, 40.0% (19.3% to 60.0%) were in hospital 72 hours after admission, while none was diagnosed with heart failure or died within 28 days of outcome.
Converting the percentages, 155 unvaccinated with 7 heart failures and 3 deaths; 48 Biontech with 1 heart failure and 1 death; and 21 Moderna vaccinees was simply too few to register a heart failure or death, because 2% of 21 is only 0.4.
Again, these are the numbers for all of Denmark for the year. For comparison, here's what Covid did in the same time frame:
External Quote:
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. Nevertheless, SARS-CoV-2 infection was associated with a 14-fold increased risk of cardiac arrest or death in the 28 days after a positive SARS-CoV-2 test compared with uninfected follow-up.
2 people died in the hospital of myocarditis with a vaccination; 1532 people died with Covid.
Getting vaccinated looks like a pretty good deal.