It’s been clear that the Pfizer and Moderna covid vaccines cause myocarditis for some time. What hasn’t been clear, though, is whether the risk of myocarditis after vaccination is greater than it is after infection. If the risk after infection is even greater than it is after vaccination, then a pretty good case can be made for not worrying too much about vaccine induced myocarditis, under the assumption that almost everyone who doesn’t get vaccinated is sooner or later going to get covid, and thereby be exposed to the risk of post-infection myocarditis.
If, on the other hand, the risk is greater after vaccination, then a more careful weighing of risks needs to be done. For the large segments of the population that face infinitesimal personal risk from covid-19 (basically everyone under 40 years of age who is not overweight and who doesn’t have any underlying health issues), even a small risk of serious disease from the vaccines could be enough to tip the scales in favour of not vaccinating.
And myocarditis is a serious disease, make no mistake. Lately, I’ve been hearing this sentence alot: “but the myocarditis caused by the covid vaccines is mild!”. I’d never heard of “mild” myocarditis pre-covid. Pre-covid, myocarditis was always considered a serious disease. What the people saying this mean is that the patients admitted to hospital with myocarditis after vaccination are usually able to go home after a few days, and don’t generally end up in an ICU. Which is true.
But we don’t say that most heart attacks are “mild” just because they don’t result in a stay in an ICU, and just because the patient is usually able to leave the hospital within a week. A heart attack is a heart attack, and is by definition serious. The same goes for myocarditis. Our heart muscles are not very good at repairing themselves, and it is impossible to know today the extent to which an episode of vaccine induced myocarditis increases the person’s future risk of serious long-term complications, such as chronic heart failure or atrial fibrillation.
So, myocarditis is always serious, regardless of whether it puts you in an ICU or not, and we need to know whether the risk of myocarditis caused by the vaccines is greater than the risk caused by infection.
Thankfully, a study was recently published in Nature Medicine that helps us to answer that question. What the researchers did was to gather data from everyone in the UK over the age of 16 who was vaccinated against covid-19 between December 2020 and August 2021. This works out to about 40 million people (more than half the UK population). For this massive cohort, data was then gathered on myocarditis events and on positive covid tests. 8% of the 40 million people had a positive covid test during the study period. The objective of the study was to see what the risk of myocarditis was within 28 days of vaccination vs infection, and relate that to the background rate of myocarditis.
There is one big problem with taking the numbers in this study at face value, and that is that it used a positive covid test as the indicator for covid infection. But we know that up to half of all covid-infections are asymptomatic, and on top of that there is an unkown number of people who have symptoms but don’t take the test. So the true number of infections is likely to be at least twice as high as the test-confirmed infections. This creates an unfair comparison when comparing with the vaccines, because we know about everyone who gets the vaccine. There aren’t lots of people who have been secretly vaccinated, and aren’t included in the statistics. So whatever risk rate we get for myocarditis after infection should probably be halved, to more accurately reflect reality.
Anyway, let’s get to the results.
The first thing that is important to note is that the relative risk of myocarditis after vaccination vs infection appears to vary massively depending on how old you are. Among people over the age of 40, there was no sign that the vaccines increased risk of myocarditis at all. A positive covid-19 test, on the other hand, increased the risk 12-fold in this group. So for people over the age of 40, the risk of myocarditis after infection was much higher than the risk after vaccination.
Among people between 16 and 40 years of age, however, the situation was very different. In this group, the 28 day risk of getting myocarditis after a positive covid-test was “only” increased four-fold. The risk after the first dose of the Pfizer vaccine was increased two-fold, while the risk after the first dose of the Moderna vaccine increased four-fold.
Let’s remember that the the covid test is probably only catching half, at best, of all infections, so the real risk increase after infection is more like two-fold, not four-fold. In other words, in people under 40, the first dose of the Pfizer vaccine causes roughly the same number of cases of myocarditis as an actual covid infection, while the first dose of the Moderna vaccine causes roughly twice as many cases of myocarditis.
Ok, so let’s get to the second dose. The second dose of the Pfizer vaccine increased the risk of myocarditis three-fold, while the risk after the second dose of the Moderna vaccine was increased 21-fold!
It’s safe to conclude here that the decision, a few months back, by authorities in many European countries to put a hold on giving the Moderna vaccine to anyone under the age of 30 was wise. One thing that is clear is that the second dose, of both the Pfizer and Moderna vaccine, increases risk substantially when compared with the risk seen after the first dose. Which really begs the question how smart it is to recommend a third dose to people under the age of 40. It’s reasonable to think that the third dose might increase the risk of myocarditis even further.
One thing that is clear from the data in this study is that there is a strong age gradient, with risk of myocarditis after vaccination increasing massively with decreasing age. In fact, for the youngest group (16-29 years), the risk of myocarditis after getting the second dose of the Moderna vaccine was increased 74-fold!
Considering that decreasing age also means decreasing risk of a bad outcome from covid (including decreasing risk of myocarditis after covid), it is reasonable to think that there is an inflection point at which the harms of vaccination outweigh the benefits. On top of that, there is evidence that increasing the number of doses increases the risk of myocarditis. With those two factors in mind, it’s my measured opinion that giving boosters to healthy young people, and especially to children, is nuts. On top of that, many, if not most, young adults and children have already had covid, and therefore have as good immunity as it’s possible to get, so boosting literally exposes them to risk of harm without any possibility of benefit. When the benefits of vaccination are zero, any non-zero risk is unacceptable.
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