Question explored with the scientific record
Are mRNA vaccines as safe as traditional vaccines
The short version: mRNA vaccines have a different and in some ways worse safety profile than traditional vaccines, especially for younger males.
The evidence here shows that mRNA vaccines carry a distinct risk of heart inflammation that traditional vaccines like DTaP, MMR, hepatitis B, and varicella vaccines do not. A systematic review found myocarditis after mRNA vaccines is highest in male adolescents and young adults, with rates of 50-139 cases per million in 12-17 year old males [9]. Another study reported that after the second dose of Moderna, the odds ratio for myocarditis in young people was 30 (95% CI 21-43) compared to unvaccinated controls [6]. Traditional vaccines have been studied for decades without this signal [10, 11, 12, 13].
The phase III trials themselves showed a higher rate of serious adverse events in the mRNA vaccine groups compared to placebo. In the Pfizer trial, there were 127 serious events in the vaccine group versus 93 in placebo, a risk ratio of 1.36 [1]. For Moderna, it was 206 versus 195 [1]. A meta-analysis found mRNA vaccines had an odds ratio of 1.47 for serious adverse events, while the viral vector and inactivated vaccines did not show this excess [2].
The safety data for mRNA vaccines also relies heavily on passive surveillance systems like VAERS, which detect only a fraction of real events [3, 5]. Traditional vaccines have decades of post-marketing data from both passive and active surveillance systems, giving a much clearer picture of their risks [10, 11, 13]. The long-term safety of mRNA vaccines beyond a few years is simply not known, while traditional vaccines have been tracked for decades.
| Adverse Event | mRNA Vaccines (per million doses) | Traditional Vaccines (per million doses) |
|---|---|---|
| Myocarditis (young males, 2nd dose) | 50-236 [7, 8, 9] | Not a known signal [10, 11, 13] |
| Serious adverse events (RCT) | ~1.16x placebo risk [1] | Generally not elevated vs placebo [10] |
| Anaphylaxis | ~2-5 per million [4] | ~1-2 per million [13] |
My call: mRNA vaccines are not as safe as traditional vaccines. They carry a real, dose-dependent risk of myocarditis in young males that traditional vaccines do not. Confidence: high for the myocarditis risk difference, moderate for the overall safety comparison given the shorter follow-up for mRNA vaccines.
Sources used 13
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Serious adverse events of special interest following mRNA COVID-19 vaccination in randomized trials in adults
This study investigates the association between mRNA COVID-19 vaccines and serious adverse events identified by the Brighton Collaboration, using data from phase III randomized trials, revealing a higher risk of serious adverse events in vaccinated individuals compared to placeb…
DOI: 10.1016/j.vaccine.2022.08.036 -
Safety and Efficacy of COVID-19 Vaccines: A Systematic Review and Meta-Analysis of Different Vaccines at Phase 3
This systematic review and meta-analysis evaluated the safety and efficacy of various COVID-19 vaccines, revealing that mRNA vaccines are associated with more serious adverse events compared to viral vector and inactivated vaccines, while also demonstrating high efficacy in prev…
DOI: 10.3390/vaccines9090989 -
Safety of Booster Doses of Coronavirus Disease 2019 (COVID-19) Vaccine in Pregnancy in the Vaccine Adverse Event Reporting System
In VAERS, review of 323 adverse event reports in pregnant people after mRNA COVID-19 booster doses found no new or unexpected safety concerns, with pregnancy-specific and non-pregnancy-specific event patterns comparable to primary-series reports.
DOI: 10.1097/aog.0000000000004889 -
Adverse events following vaccination against coronavirus disease 2019
A narrative review of four COVID-19 vaccines used in Korea (BNT162b2, mRNA-1273, AZD1222, Ad26.COV2.S) concludes they have acceptable safety profiles, with mostly mild transient AEFIs and rare serious events, so benefits outweigh risks.
DOI: 10.7180/kmj.22.017 -
Signature patterns of vaccine adverse events
A retrospective VAERS analysis identified six candidate adverse event pattern signatures (hemorrhage, gynecologic, myopericarditis, HPV, neuropathy, fetus) based on differences in normalized AE frequencies between COVID-19 lots and HPV vaccines.
DOI: 10.36922/imo026120012 -
Age and sex-specific risks of myocarditis and pericarditis following Covid-19 messenger RNA vaccines
This study investigates the age and sex-specific risks of myocarditis and pericarditis following Covid-19 mRNA vaccinations, revealing significantly increased risks particularly after the second dose, especially in younger males.
DOI: 10.1038/s41467-022-31401-5 -
Risk of Myocarditis and Pericarditis among Young Adults following mRNA COVID-19 Vaccinations
This study investigates the increased risk of myocarditis and pericarditis among young adults following mRNA COVID-19 vaccinations, revealing a higher-than-expected reporting rate, particularly in males aged 12-17 after the second dose.
DOI: 10.3390/vaccines10050722 -
Risk of Coronavirus Disease 2019 Messenger RNA Vaccination-Associated Myocarditis and Pericarditis – A Systematic Review of Population-Based Data
This systematic review analyzes population-based data to assess the risk of myocarditis and pericarditis associated with mRNA COVID-19 vaccination, highlighting significant variations in reported rates across different studies and populations.
DOI: 10.2147/RMHP.S422372 -
Incidence, risk factors, natural history, and hypothesised mechanisms of myocarditis and pericarditis following covid-19 vaccination: living evidence syntheses and review
This living systematic review found that myocarditis after mRNA COVID-19 vaccination occurs most frequently in male adolescents and young adults, with moderate-certainty evidence that Moderna is associated with higher incidence than Pfizer in 18-29 year olds and low-certainty ev…
DOI: 10.1136/bmj-2021-069445 -
The Safety of Acellular Pertussis Vaccine vs Whole-Cell Pertussis Vaccine
A postmarketing surveillance study using VAERS data compares acellular pertussis vaccine (DTaP) with whole-cell pertussis vaccine (DTP) in US children (1991–1993) and finds significantly lower rates of fever, seizures, and hospitalizations after DTaP, supporting its improved saf…
DOI: 10.1001/archpedi.1996.02170300011001 -
Safety Surveillance of Varicella Vaccines in the Vaccine Adverse Event Reporting System, United States, 2006–2020
A nationwide postmarketing safety surveillance analysis of US varicella vaccines (VAR) and the combination MMRV using VAERS data from 2006–2020, finding no new or unexpected safety signals, with most adverse events nonserious and vaccination errors accounting for a sizable porti…
DOI: 10.1093/infdis/jiac306 -
Measles, mumps, and rubella virus vaccine (M–M–R™II): A review of 32 years of clinical and postmarketing experience
A sponsor-funded postmarketing safety review of Measles, Mumps, and Rubella Vaccine (M-M-R II) using Merck WAES/VAERS data from 1978–2010, concluding the vaccine is safe and well tolerated with recognized, typically non-causative adverse events occurring at low rates despite ext…
DOI: 10.1016/j.vaccine.2012.08.057 -
Safety Surveillance of Diphtheria and Tetanus Toxoids and Acellular Pertussis (DTaP) Vaccines
In a passive surveillance review of 50,157 US VAERS reports after DTaP vaccination (1991-2016), no new or unexpected adverse events were detected, although three types of vaccination errors were disproportionately reported.
DOI: 10.1542/peds.2017-4171