Korea's reassuring vaccine data

Autopsy results reveal extremely rare sudden deaths

The mRNA COVID vaccines can cause myocarditis, which rarely leads to sudden cardiac death. The risk of vaccine myocarditis is most pronounced in teen boys receiving a second dose, and Moderna has a higher rate than Pfizer. Studies have shown substantial variation in rates because the event is very rare. Any estimate is inherently imprecise and subject to definitional and ascertainment issues. Lots of people cherry pick the studies that support their pre-conceived notions. But synthesizing the best studies, we can say that in teen boys, the rate of myocarditis is about 1-2 in 10,000 with about 1% of cases leading to death. In everyone else, the rate is much lower. This includes young children, whose risk of myocarditis is nearly non-existent, and older adults who have a very tiny risk. I have previously written about this topic for The Atlantic.

Some cases of vaccine myocarditis and vaccine-related death will be missed by our surveillance systems. This is also true of COVID, where we know many, many deaths are missed. In particular, the pandemic led to a sudden spike in cardiac deaths, including among young people. These sudden cardiac deaths are mainly due to COVID itself, and began before vaccines were available.

Vaccine skeptics and outright conspiracists have raised the idea that the shots are secretly causing tons of sudden deaths. Although this was always unlikely, not every death is fully investigated so there are knowledge gaps.

Epidemiologic studies, looking at patterns of death before and after vaccination, are one way to assess whether there are “hidden” vaccine deaths. (The gold-standard randomized controlled trials of the vaccines were also highly reassuring but couldn’t exclude very rare deaths.) The best study so far is from the UK. The authors did not find a statistically significant increase in cardiac deaths among young people post-mRNA vaccine. (COVID did lead to an increase in cardiac death among young people.) However, the result for the subgroup of men receiving a second mRNA dose did show an almost-significant effect. This rate was about 1 death for every 359,294 doses. That’s extremely small and in line with what we already know about incidence and complications of vaccine myocarditis in this group.

Now, an important new study has come out of Korea looking at vaccine myocarditis across the country. Myocarditis occurred in 1 in 100,000 people overall. The authors found a lower rate of vaccine myocarditis in teen boys than other studies (~1 in 20,000) but average severity was higher: 4.4% of myocarditis cases in their study lead to death. Again, given the rarity of these events, there is inherent imprecision. The results, however, are compatible with what we already know. This study used expert adjudication with pre-specified criteria to determine whether vaccine myocarditis occurred. This is the gold standard method compared to passive reporting or using electronic diagnosis codes without expert review.

What’s unique about this study is that the country appears to have performed autopsies on all sudden deaths that occurred after vaccination. Previous case series have already shown that autopsy can pick up occult cases of vaccine-associated death, but these reports could not calculate any sort of incidence rate. (This didn’t stop anti-vaxxers from trying to do so.)

I want to emphasize the caveat that I may be misreading the Korean analysis, but here is what the authors wrote:

To my eye, that means all cases of sudden death were autopsied. Having systematic autopsy data is rare in any country. Florida has made dramatic and politicized moves to supposedly “investigate” sudden deaths related to the vaccine. Korea has done just that.

The researchers found 8 sudden cardiac deaths due to vaccine myocarditis (21 deaths overall when including clinically identified cases). This is just an extremely low number of occult deaths in a population of 44 million vaccinees. We can rest assured that our general understanding of the cardiac risks of mRNA vaccines is correct: vaccine myocarditis is rare, deaths from myocarditis rarer still, and the cardiac risks from the virus are much larger (to say nothing of the many other risks of COVID). Vaccine myocarditis, however, is unevenly distributed in the population and special consideration should be given to males age 12-25. Notably, however, none of the sudden cardiac deaths in the Korean study were in teens despite 2 million of them getting inoculated. The two youngest cases were ages 22 and 25.

Whenever I write about myocarditis, I receive a bunch of angry responses about vaccine mandates. To be clear, I do not set vaccine policy anywhere on Earth. When it comes to children and very young adults (under age 30), serious complications of COVID are rare but real, as are serious complications from the vaccine. This makes a quantitative cost-benefit analysis challenging as any estimate is highly imprecise. But my view is that a single Pfizer dose in teen boys was probably the best bang for our buck, although this is not what some public health authorities and mandates dictated.

I also get yelled at about boosters in vaccinated and/or previously-infected individuals. The greatest benefit from the vaccines came from receiving a primary series before infection. There was a vital period just after the vaccines came out when uptake was critical to preventing morbidity and mortality. I strongly encouraged vaccination during that time period, and I’m proud of that. Other doctors did everything they could to raise suspicions of the vaccine and slow uptake. Now they want to take a victory lap because the situation has changed, and the absolute benefit of incoculation has gone down. It should go without saying that we can’t bring back the dead. The very least we can do is not erase our memory of them. So many COVID deaths could have been prevented with better vaccine uptake (including third shots among high risk during Delta/Omicron).

It’s easy to say today that repeated boosters in low-risk people with widespread infection-based immunity are of questionable value. In fact, I wrote a whole article for The Atlantic about that. COVID vaccination policy is now complex and uncertain. For the highest-risk people, the benefits to boosting are still meaningful. But if we wish to continue universal boosting, I think we need to develop different vaccines for that.

The mRNA shots are among the more dangerous vaccines we use. But they are also among the safest therapeutics overall. The average person might not understand the ubiquitous dangers of our common drugs and procedures. The mRNA shots are about as safe as or safer than Tylenol. Eight sudden deaths sounds scary, I understand. Let’s not minimize any death. But like all interventions, we need to weigh benefits and risks. The pandemic was a moment of incredible danger—even for young, healthy people like myself. Developing highly-effective vaccines in record time while still subjecting them to large, rigorous randomized trials was a remarkable feat. For all of history, the only possible outcome from the emergence of a highly-contagious novel infection was having it rip through an immune-naive population. But for the first time, we could provide a much safer form of immunity before that happened to everyone. We had to learn about the vaccines as we went along. I wish we started with a decade of data on day 1, but that’s not how time works. The COVID vaccines were a life-saving triumph.