The last five years have been filled with stress and fraught with complex decisions for parents. And the issues aren’t going away anytime soon. The pandemic brought health and parenting decisions to what has sometimes felt like a cataclysmic intersection. Even with all my training and background knowledge, it has frequently felt like there was no way to know what the right decision was for my family and my kids. I know many others have felt the same. Especially those who don’t feel as comfortable around healthcare.
One of the most common questions my friends have asked me over the past 4 years, since the first COVID-19 vaccines came out, was “Are they safe?”. First, it was for themselves. And then, as the younger age groups were approved, it was for their kids. And my resounding answer was, and still is, YES. Yes, they are safe. But no, it’s not 100%. Nothing in life is.
So let’s dig into that a little bit more. Specifically, looking at the risk of myocarditis which has been in the news a lot over the past few years. Myocarditis is simply inflammation of the heart muscle. When the COVID vaccines were first approved, there was no hint of these cardiac risks. So when they started making the news, there was an outcry. Claiming the vaccines weren’t fully tested. Claiming the process was rushed. And let me reassure you. They were tested. And the process was not rushed. So what happened? And do you need to be worried about your kid’s heart?
First, let’s talk a little bit about what the vaccine development process looks like. Vaccine development looks a lot like the development process for any pharmaceutical. First, scientists spend years working on background research. For the COVID-19 vaccines, this meant decades of research learning about coronaviruses and mRNA. Most of that time, with no knowledge of what the future was sending our way with a coronavirus pandemic barreling towards us. Then, once researchers believed they had something in the lab that could protect people, they moved onto animal studies. At this step, scientists are trying to demonstrate that their vaccine causes the immune system to stand up and go to work. If it works well, they get to move onto clinical trials in people. The FDA process requires three separate stages of clinical trials. The first is a very small study, usually less than 100 people, who receive the vaccine in the Phase 1 trial. If this group shows no concerning safety issues and also shows that the immune system is responding (like had already been shown in animals), then the vaccine moves onto Phase 2 trials. They increase the number of participants from less than a hundred to several hundred people. Here, they are still monitoring for potential adverse reactions but what they are really looking for is an immune response or evidence that the vaccine is working as expected. Researchers are testing to be sure the vaccine actually protects people from the disease they are trying to prevent. And then, if the Phase 2 results look good, the final Phase 3 clinical trial will increase the number of individuals into the thousands. Here, they are confirming both the immune response as well as looking for the less common side effects that they couldn’t identify with only a few hundred individuals.
Once a vaccine successfully navigates all the research and clinical trial phases, it goes up for approval. And this is a multi-step process as well. It starts with the FDA. They scrutinize the clinical trial data. They check on the proposed manufacturing plans to ensure the company has the capability to reliably and safely produce the vaccine at scale. They test vaccines from multiple “lots,” or groups of the vaccine that the company produced to prove they could, making sure each lot is exactly the same. They frequently call on independent scientific and public health experts to review the vaccine publicly through something the FDA calls the Vaccines and Related Biological Products Advisory Committee (VRBPAC). Then, if the FDA says everything looks good and gives the green light, the vaccine moves to the CDC for review. The CDC has a group of experts called the Advisory Committee on Immunization Practices (ACIP) that further breaks down the safety and efficacy data. They consider the public health impact of the disease (how many people can benefit), how it works in different groups (different age brackets, different exposure populations like people who work in a specific setting or who have a specific predisposition to the illness like someone traveling to a country with a lot of infectious disease risk). Once the ACIP says the vaccine looks good, and who they think should use it, the CDC director issues their approval and it officially becomes part of the U.S. vaccine schedule.
Normally, this process takes years. Sometimes more than a decade. So why should we trust a process that seemingly only took a year? Well, to do that, you need to understand why it usually takes so long and why this went faster. First, there are three big reasons vaccine trials take so long: 1) Money; 2) Recruiting Limitations; and 3) Time to see effects. Vaccine trials cost a lot of money so pharmaceutical companies tend to spread them out over time so they don’t have to commit as much money at once. For the COVID-19 vaccines trials, this wasn’t an issue. Multiple government and private institutions, across the world, came together to ensure the money was there to make these vaccines. They committed billions of dollars to ensure the research and production was developed as fast as possible. The second limitation, recruiting, slows trials down because, for most diseases, people aren’t lining up to be guinea pigs. It takes a lot of time to advertise trials, screen participants, and get sufficient numbers of qualified people enrolled in the trial. Once again, this wasn’t a problem with COVID-19. We were in the middle of a pandemic that was all over the news. Everyone knew about these trials. Companies like Pfizer and Moderna had long interest lists, full of people who wanted to be part of the clinical trials. My own daughter was on one of these lists, just in case they ended up opening a study site near us. So clinical trials were able to fill their numbers fast, way faster than any normal trial would have done. And the final issue is time. And here is where people get worried. Did the trials give it enough time? The first thing to understand here is that almost all possible side effects from vaccines will appear within hours or days. And beyond that, 6 weeks is the magical number. If a vaccine is going to have an adverse reaction, we will pretty much always see it within 6 weeks. So, because the trials enrolled people so quickly, they had plenty of time to follow people for even longer than 6 weeks. Pfizer alone enrolled over 46,000 participants in their trial in just 6 months. And followed them for at least 10 weeks. That was plenty of time to see side effects.
So long story short, while the COVID-19 vaccines were approved very fast by normal standards, it was not because they cut corners or skipped steps. It was because the scientists, funding agencies, pharmaceutical companies, and even the public stepped up and made things work. If you want to see a great breakdown of the whole mRNA vaccine timeline, the Mayo Clinic has put together a great website that walks you through each step (https://www.mayoclinic.org/diseases-conditions/history-disease-outbreaks-vaccine-timeline/covid-19)
So then why didn’t the trials discover this whole myocarditis issue? Well, 40+ thousand people may sound like a lot (or over 70,000 if we count the Moderna trial too), it really is nothing compared to the 8 billion people on earth. In reality, they studied just 0.0008% of the world’s population. That leaves a lot of variation that the clinical studies couldn’t look at. Clinical trials are really good at finding the common side effects. And even the more common rare effects. But they can still miss truly rare effects. Because of this, all pharmaceuticals, including vaccines, undergo their Phase 4 clinical trials, also known as post-market surveillance. The pharmaceutical companies, the FDA, and even independent scientists like me study medications for decades long after they become available to the general public. And what we’re looking for is new side effects that the clinical trials missed. Thus, the flag was raised around myocarditis.
And raised it was. Just a quick search on PubMed, the NIH’s giant databases of all scientific research articles dealing with any kind of medical or health effects, finds over 700 research articles looking at the relationship between the COVID-19 mRNA vaccines and myocarditis in one way or another. So scientists have taken this very seriously. And have sought to get a better handle on what the risk really is.
A lot of the research is passive surveillance. There are two systems that anyone (you, me, your doctor, a pharmacist, etc.) can submit suspected adverse reactions. The first is specific to vaccines: the Vaccine Adverse Event Reporting System (VAERS). The second is for all pharmaceuticals: the FDA Adverse Event Reporting System (FAERS). Anything can be reported, from something as trivial as a hang nail to something as serious as a death. There doesn’t have to be any proof that the event is linked to the vaccine. It just has to have occurred after vaccine was given. These sites are great for detected adverse event signals. In other words, they are great for finding potential things to investigate. Scientists look at these systems to see if anything is getting reported by multiple people who had the same vaccine. If they find something, they then take that potential side effect and look for other ways to corroborate it. VAERS and FAERS are messy. There are a LOT of false positives when looking at passive surveillance data. Because many people will report absolutely anything after they get a vaccine. Even if it is very clearly caused by something else. So we need to be careful with the passive surveillance data. But it’s a great way to find things that we should investigate further. Things like myocarditis.
After scientists began to suspect that myocarditis might be an adverse reaction, they took it and looked for other data sources to study. Researchers used a lot of different study designs: case-reports, cohorts studies, clinical trials, active surveillance, etc. And the overwhelming conclusion was that yes, the myocarditis signal that was detected in VAERS was real.
So then, scientists sought quantify the risk. Some scientists even performed what are called meta-analyses, where they scour the scientific literature for anything that has been published and combine all the results to come up with a single risk estimate. The benefits of this is that it helps see if all the studies being conducted are agreeing with each other or if the results are all over the place, suggesting we don’t actually understand the results yet. And these meta-analyses came back showing what we long had suspected by this point – the risk of myocarditis from the vaccine was real.
But what it also found is that the risk was actually focused in a single group: young adult and adolescent males (generally speaking, 12-40 years old) who were receiving their second vaccine dose. The risk is small, only about 10 cases of myocarditis out of every 100,000 vaccine doses in 12-17 year old boys and about 20 cases of myocarditis out of every 100,000 vaccine doses in 18-24 year old men. So the risk is rare. Which is why it wasn’t identified during the clinical trials. There simple weren’t enough people in the clinical trials to see something that happens that infrequently.
Since we have confirmed that the myocarditis risk is real, scientists have moved on to trying to understand the reason for the myocarditis cases. One thing they have noticed is that individuals that get myocarditis have significantly higher levels of circulating SARS-CoV-2 spike proteins compared to individuals who did not develop myocarditis. Basically, this means that the protein the vaccine tells our body to make, the protein our immune system then attacks to learn how to defend itself should it ever be infected with COVID-19, was not being successfully grabbed and removed by our immune system in people who developed myocarditis. Why it wasn’t being removed is still unclear. Are people with myocarditis making more of the spike protein than people without? Or maybe people with myocarditis are not showing as strong responses from some specific part of their immune system? Scientists are still digging. They have also launched a large cohort study designed to pull in cases of vaccine-induced myocarditis as well as a comparator group without myocarditis called the COVID Vaccine-Associated Myocarditis/Pericarditis (CAMP) study. This study is still enrolling participants but hopefully we will have some preliminary results soon.
But to fully understand the risk, you want to compare it to the risk of myocarditis if you contract COVID-19 without being vaccinated, because that is the true comparison group. At this point, pretty much everyone has been exposed to COVID-19. So if you aren’t vaccinated, it is pretty much a guarantee that you’ll get it. Even vaccinated individuals are likely to get it at some point, just a more mild version. And since there is evidence that the risk of myocarditis is associated with the amount of spike protein in body, it is entirely reasonable to assume that more severe cases have more risk of myocarditis.
So are we worried about myocarditis if we get COVID-19? The answer, just like it is for the vaccine, is Yes. So, the same as we did for the vaccine, let’s try to quantify the risk. We know the vaccine causes between 10 and 20 cases of myocarditis for every 100,000 young men who get the vaccine. So let’s use the same comparison for the COVID-19 virus. Researchers out of the CDC found that for every 100,000 individuals who develop COVID-19, 150 cases of myocarditis result. So the risk is roughly 15 times higher for viral myocarditis compared to vaccine-induced myocarditis.
Another thing to consider is the severity of the myocarditis. The vast majority of myocarditis cases will subside with little to no long-term effects. However, occasionally, myocarditis can be severe. Severe cases can result in a weakened heart and, in the most extreme cases, death. What researchers have found is that the risk of severe myocarditis side effects is significantly greater in viral myocarditis than in vaccine-induced myocarditis. One study found a 92% lower risk of death in people who had vaccine-induced myocarditis compared to people who had viral myocarditis.
So the take home message after digging through all the details is this: Yes, the vaccine could result in myocarditis but the risks are far greater for people who contract the virus without vaccination. So here is what I say to parents who ask me what I would do. If your kid is younger or a girl, go for it! The risk is mainly in adolescent and young adult males. So myocarditis doesn’t worry me for young kids or for girls. But what if you have a 16 year old boy? Then here is the question I think you should ask yourself: Do I want to guarantee them a low risk of some mild heart problems and an even lower risk of severe heart problems by getting the vaccine OR do I want to roll the dice and hope they never get COVID-19 so there is no risk but if I’m wrong and they do catch the virus, their risk of negative myocarditis outcomes is even higher? And given how prevalent COVID-19 has become around the world over the past 5 years, the chances of never getting it is VERY low.
For me, it wasn’t even a question. My daughter got it the minute the vaccine was available, long before we even suspected the myocarditis risk. And I would do it again in a heartbeat. Partially because she was a girl and just a toddler, so the risk was tiny. But also because the risk from the virus scares me way more than the risk from the vaccine. And because of this, I got the vaccine and have gotten every booster I could, including one while I was 8 months pregnant with my son. My son got his vaccine and each booster as soon as he reached 6 months old. And my husband, who was in the “under 40” male group and therefore at higher risk, went in and got his vaccines without any hesitation.
So it ultimately is up to you where you think the greater risk lies. That is our constant challenge as parents, figuring out what risks are worth taking and which to avoid in order to raise happy, healthy kids. I deemed the vaccine to have greater benefits and fewer risks than the virus for my family. And I think the science definitely supports that. But it doesn’t support zero risk. So as a parent, it’s up to you to read through the data and come to your own decision.
As always, remember, I am not a medical doctor and I am not your child’s pediatrician. I encourage you to talk this over with your pediatrician if you are concerned. And review the websites I have cited below. I am just a mom and an epidemiologist, out to summarize the state of the science for you so you can make better informed decisions for your own family.
References:
https://www.pfizer.com/science/coronavirus/vaccine/about-our-landmark-trial
https://www.mayoclinic.org/diseases-conditions/history-disease-outbreaks-vaccine-timeline/covid-19
https://www.cdc.gov/vaccines/basics/how-developed-approved.html
https://archive.cdc.gov/www_cdc_gov/coronavirus/2019-ncov/vaccines/expect/after.html
Kitano T, Salmon DA, Dudley MZ, Saldanha IJ, Thompson DA, Engineer L. Age- and sex-stratified risks of myocarditis and pericarditis attributable to COVID-19 vaccination: a systematic review and meta-analysis. Epidemiol Rev. 2025 Jan 10;47(1):1-11. doi: 10.1093/epirev/mxae007. PMID: 39673764. https://pubmed.ncbi.nlm.nih.gov/39673764/
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Yonker LM, Swank Z, Bartsch YC, Burns MD, Kane A, Boribong BP, Davis JP, Loiselle M, Novak T, Senussi Y, Cheng CA, Burgess E, Edlow AG, Chou J, Dionne A, Balaguru D, Lahoud-Rahme M, Arditi M, Julg B, Randolph AG, Alter G, Fasano A, Walt DR. Circulating Spike Protein Detected in Post-COVID-19 mRNA Vaccine Myocarditis. Circulation. 2023 Mar 14;147(11):867-876. doi: 10.1161/CIRCULATIONAHA.122.061025. Epub 2023 Jan 4. PMID: 36597886; PMCID: PMC10010667. https://pubmed.ncbi.nlm.nih.gov/36597886/
Lai FTT, Chan EWW, Huang L, Cheung CL, Chui CSL, Li X, Wan EYF, Wong CKH, Chan EWY, Yiu KH, Wong ICK. Prognosis of Myocarditis Developing After mRNA COVID-19 Vaccination Compared With Viral Myocarditis. J Am Coll Cardiol. 2022 Dec 13;80(24):2255-2265. doi: 10.1016/j.jacc.2022.09.049. PMID: 36480967; PMCID: PMC9721305. https://pubmed.ncbi.nlm.nih.gov/36480967/
Quite a lot of information but great reading.