New Study – mRNA Vaccines Safe


Science-Based Medicine

By Steven Novella

After more than 298 million doses give, the side effects of the mRNA vaccines are minimal and transient.

As we often discuss on SBM (most recently yesterday), clinical decision-making often follows a risk vs benefit model. For each medical intervention we need to consider both the risks and benefits of that intervention compared to other alternatives, including doing nothing. That is what we would consider an analytical approach, looking at all the data quantitatively. However, the typical human intuitive approach is to just consider the risks of the one intervention being considered. We tend to be risk-averse, and more averse to active risks than passive risks (from doing something rather than from not doing something).

Vaccines in general have perhaps the overall best risk vs benefit ratio of any type of medical intervention. The benefits can be profound and multi-layered, making one highly resistant to serious illness, and reducing the risk of spread and the emergence of new variants. A successful vaccine program can even eliminate an infectious illness from a community and in some cases (like smallpox) eradicate it from the world. The risks, meanwhile, are statistically minimal – but they are not zero.

Vaccine hesitancy remains a problem, however, mostly fueled by misinformation which is effective because people are risk averse. Fortunately it’s possible to gather massive data sets regarding most vaccines because they are a public health measure and are therefore given to many people. Getting vaccinated is also a recorded event and so it’s possible to track for correlations.

In late 2020, about a year into the COVID pandemic, two mRNA vaccines were introduced, Pfizer and Moderna. This is not an entirely new technology, but these were the first mRNA-based vaccines. They were both given emergency use authorization (EUA) based upon large clinical trials with tens of thousands of subjects followed over 3-6 months. Because we were (and are) in the middle of a serious pandemic the vaccines were rolled out based on this EUA prior to going through the full approval process, which took another 8-9 months. Some were concerned that a new type of vaccine was being rushed into people’s arms without adequate testing. This was never a legitimate concern – the research had been completed prior to the EUA and the delay to full authorization was merely due to red tape. Also, vaccine side effects typically emerge within 3 months of getting vaccinated, so while no one could ever promise zero risk, we could make a rational risk vs benefit assessment. These are highly effective vaccines with minimal risks.

Now, however, we have the benefit of being more than a year into the COVID vaccine program. More than 298 million doses of mRNA vaccines have been given in the US alone, and this represents a massive collection of data we can use to monitor the safety of these vaccines. That is just what a recently published study in The Lancet does. They look at two reporting systems, VAERS and v-safe. VAERS is the Vaccine Adverse Event Reporting System which is a passive system, people choose to report their vaccine side effects. V-safe, on the other hand, is a voluntary but active monitoring system, where people are sent texts and reminded to use an app to report their side effects in the days following a vaccine dose. Here is the quick summary of what they found:

VAERS processed 340 522 reports: 313 499 (92·1%) were non-serious, 22 527 (6·6%) were serious (non-death), and 4496 (1·3%) were deaths. Over half of 7 914 583 v-safe participants self-reported local and systemic reactogenicity, more frequently after dose two (4 068 447 [71·7%] of 5 674 420 participants for local reactogenicity and 4 018 920 [70·8%] for systemic) than after dose one (4 644 989 [68·6%] of 6 775 515 participants for local reactogenicity and 3 573 429 [52·7%] for systemic).

After nearly 300 million doses give there were 340,522 reported side effects in VAERS, but the vast majority of these (92.1%) were mild. There were 22,527 side effects that were considered serious, but these were mostly transient. Further, there were no new phenomena revealed in this data. We already knew about the rare side effect of myocarditis and rare serious allergic reactions. I wrote previously about the myocarditis side effect, which is rare and transitory. Anaphylaxis is also rare (0.025%) and all subjects recovered.

What about those 4,496 deaths? The anti-vaccine cranks have spread a lot of fear about those deaths, falsely assuming that they were caused by the vaccine. Of course, this is a correlation only. What we need to ask is – what would be the background death rate of the same population over a six month period? It turns out it would be exactly the same. Most of those deaths were in the older population (>60) who have a higher background mortality. The study detected no signal at all of any bump or change in the background mortality rate. The mRNA vaccines, put simply, do not increase the risk of death.

It is also worth pointing out that this data, again from over 298 million doses, was very similar to the data found in the clinical trials used to obtain EUA. What was new since then was the data on myocarditis and anaphylaxis, because these adverse events were too rare to pick up in the initial trials. But these side effects were known about before this current study, which did not detect any new risk signals.

What all this means is that the mRNA vaccines are extremely safe. Most people can expect a day or two of uncomfortable symptoms, but transient and not serious. Meanwhile, COVID itself is a serious illness. The risks from getting COVID, even if you are not in a vulnerable population, are orders of magnitude greater than the risks of the vaccine. The risk vs benefit analysis here is a no-brainer. Get vaccinated.

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking – also called The Skeptics Guide to the Universe.