The Latest on Myocarditis After COVID Vaccination

Overall good news, but plenty of questions remain.

At this point, it is clear that the rate of myocarditis after vaccination with mRNA vaccines, particularly among young men, is higher than the background rate.

It is not much higher. The CDC estimates the risk of myocarditis after mRNA vaccination is 70 per 1,000,000 doses given among boys aged 16-17 years, who appear to be at the highest risk.  The risk is negligible among girls and older adults.

The chance that any given boy will develop myocarditis after COVID-19 vaccination is extremely low, and for the most part lower than his chance of developing myocarditis after COVID-19 infection, as you can see here.

But… what if it happens? What can we expect?

We get the most detailed data yet on this question from this paper, appearing in Circulation, which examines 139 children and young adults with vaccine-associated myocarditis from 26 centers across the US and Canada.

Patient info

OK let’s start with some info about the patients. About half were aged 12-16, the rest were between ages 16 and 20. At the time this data was collected, vaccines were not approved for those under age 12 yet. The cohort is skewed heavily towards males, and while there isn’t a control group – unless males were substantially more likely to get vaccinated than females in the catchment areas of these medical centers, this is further confirmation that being a male is a significant risk factor for vaccine-associated myocarditis.

Fully 90% of these cases occurred after the second dose of the vaccine – a median of 2 days after, though one patient presented 22 days after.

OK – not many kids got myocarditis after the first dose of vaccine, but 12 did, and there’s an interesting finding here.

Kids with myocarditis after the first dose were more likely to have been previously infected with SARS-CoV-2.

Of the 12 kids who got myocarditis after the first dose of the vaccine, half had evidence of prior covid infection based upon history or antibodies. Just 10% of kids in the overall study had evidence of prior covid infection. Taken together, this strongly suggests this is an immune phenomenon, not an idiopathic reaction to some vaccine constituent.

The main symptom? Chest pain in virtually all the kids.  Associated symptoms included fever in 30%, and shortness of breath in 30%. Palpitations, rash, and conjunctivitis were relatively rare.

Treatments were variable, but most kids got NSAIDs. A good number received IVIG or steroids.

Now, to be part of this case series, you had to have received a coronavirus vaccine, be hospitalized at one of these centers, and have an elevated troponin. So I want to point out the obvious here – we are seeing what might be considered the worst cases of vaccine-induced myocarditis – we can’t really make inferences about the absolute incidence of the condition from this data.

So how bad is the worst post-vaccine myocarditis? The good news is that there were no deaths associated with the condition, and no child was sick enough to require extra-corporeal membrane oxygenation (ECMO).

About 20% spent at least some time in the ICU, but, based on the fact that just 2 kids received inotropes, I get the sense this was more precautionary than anything else.

Still, there were some concerning findings.

This image, showing a rhythm strip of a 15-second run of non-sustained Vtach in a seventeen year old is enough to make the sturdiest electrophysiologist nervous.

Rhythm strip of a boy with post-vaccine myocarditis

And this EKG, showing diffuse ST-elevations, might prompt a call to the cath lab just in case.

EKG from a boy with myocarditis after vaccination

And while most kids had normal cardiac function on Echo, 20% had reduced function.

In sum, the sickest of the sick with vaccine-associated myocarditis did pretty well. Of course, making it out of the hospital alive does not mean all is well. Longer-term follow-up of these kids to see how the event might affect their physical functioning, ability to play sports, and long-term health outcomes is critical. Further evaluation of the impact of prior infection on vaccine outcomes is reasonable.

But all told, this is positive news. The robust immune response engendered by these vaccines is not without side-effects, but we have to resist the urge to compare the effects of vaccine to the effects of no vaccine. Given the contagiousness of SARS-CoV-2, we need to compare the effects of the vaccine to the effects of COVID itself. Because in effect, that is the choice we all have to make. I hope this makes the decision a little more clear. 

A version of this commentary first appeared on Medscape.com.