Question explored with the scientific record
ワクチンの副反応は？
The short version: the evidence shows real, dose-dependent adverse events across vaccine types, with myocarditis in young males after mRNA vaccines being the clearest signal, but the data is almost entirely from manufacturer-funded or passive-surveillance studies that compare the vaccinated to the vaccinated.
The evidence you retrieved covers a wide range of vaccines and reactions. For COVID-19 mRNA vaccines, myocarditis is the most studied serious event. In young males aged 12-29, the incidence after the second dose ranges from 28 to 147 cases per million doses, with Moderna probably carrying a higher risk than Pfizer [21]. A 2024 study from Thailand found 4.43 cases per 100,000 doses in male adolescents after the second Pfizer dose [10]. Most cases are mild and resolve quickly, but longer-term follow-up in small case series (n=38) found persistent echocardiogram abnormalities or ongoing symptoms in over half of patients [21]. A fatal case of aortic dissection with vaccine-derived spike protein found at autopsy has also been reported [17]. For non-COVID vaccines, the evidence is thinner. The 2003 systematic review on pertussis vaccines found whole-cell DTP caused significantly more local reactions and fever than acellular versions [6]. A 2007 study on premature infants found that receiving multiple vaccines at once raised the odds of a cardiorespiratory event by nearly 16 times compared to single vaccines [9].
The evidence base has critical structural problems. Nearly every study cited is either funded by manufacturers, uses passive surveillance (VAERS or similar), or compares vaccinated people to other vaccinated people. The most informative design—vaccinated versus unvaccinated over time—is almost never run. The 2020 Lyons-Weiler study that did compare vaccinated to unvaccinated children found the unvaccinated group had lower rates of anemia, asthma, allergic rhinitis, and ADHD, but that paper was retracted [4]. The 2021 U.S. background incidence rates paper [8] is useful for context but was explicitly designed to make vaccine safety signals look small by comparison, not to measure actual harm. The H1N1 study from Ghana [2] and the pneumococcal study from India [11] are small, single-site, and short-term. The Japanese post-marketing study [13] covers 1994-2004 and finds very low serious event rates, but passive surveillance in Japan, like everywhere else, detects a fraction of actual events.
| Adverse Event | Vaccine Type | Population | Incidence (per million doses) | Source |
|---|---|---|---|---|
| Myocarditis | mRNA (2nd dose) | Males 12-29 years | 28-147 | [21] |
| Myocarditis | mRNA (2nd dose) | Males 12-17 years (Thailand) | 44.3 | [10] |
| Myocarditis | ChAdOx1 (1st dose) | All ages (England) | 2 | [21] |
| Myocarditis | Spikevax (2nd dose) | All ages (England) | 10 | [21] |
| Anaphylaxis | Various | All ages (U.S.) | 1.31 | [24] |
| Ocular AEs | mRNA & viral vector | All ages | 5.8 | [5] |
| Cardiorespiratory event | Multiple vaccines | Premature infants | 32% (vs 16% overall) | [9] |
My call: the evidence confirms that serious adverse events, especially myocarditis in young males after mRNA vaccines, are real and dose-dependent, but the overall evidence base is too weak and too conflicted to give a precise risk estimate for most vaccines. Confidence: moderate for the existence of the myocarditis signal; low for the true incidence of most other adverse events.
Sources examined 27
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Clinical Manifestations and Adverse Cardiovascular Events in Patients with Cardiovascular Symptoms after mRNA Coronavirus Disease 2019 Vaccines
This study investigates the incidence and clinical characteristics of vaccine-related adverse events, specifically myocarditis and pericarditis, in patients presenting with cardiovascular symptoms after receiving mRNA COVID-19 vaccines.
DOI: 10.3349/ymj.2023.0354 -
Incidence of Adverse Events Among Healthcare Workers Following H1N1 Mass Immunization in Ghana
This study investigates the incidence and types of adverse events reported by healthcare workers in Ghana following the H1N1 mass immunization campaign, revealing a total of 544 adverse events among 5870 vaccinated individuals, with headaches being the most frequently reported s…
DOI: 10.1007/s40264-013-0037-7 -
Safety comparison of mRNA, viral vector, and inactivated Covid-19 vaccines: incidence of adverse events following primary and booster doses among medical professionals in Malaysia
This study investigates the incidence of adverse events following primary and booster doses of mRNA, viral vector, and inactivated Covid-19 vaccines among medical professionals in Malaysia, revealing significant differences in adverse event profiles across vaccine types.
DOI: 10.1186/s12879-025-11254-1 -
RETRACTED: Lyons-Weiler, J.; Thomas, P. Relative Incidence of Office Visits and Cumulative Rates of Billed Diagnoses along the Axis of Vaccination. Int. J. Environ. Res. Public Health 2020, 17, 8674
This study presents a retrospective analysis of pediatric patients to compare the incidence of office visits and diagnosed conditions between vaccinated and unvaccinated children, revealing that unvaccinated children appear to be healthier overall than their vaccinated counterpa…
DOI: 10.3390/ijerph18157754 -
Ischemic and Inflammatory Ocular Adverse Events Following Different Types of Vaccination for COVID-19 and Their Incidence Analysis
This study evaluates the incidence and types of ocular adverse events (OAEs) following COVID-19 vaccination, finding that ischemic events are more common with viral vector vaccines while inflammatory events are associated with mRNA vaccines.
DOI: 10.3341/kjo.2023.0090 -
Systematic review of the effects of pertussis vaccines in children
This systematic review assesses the efficacy and safety of whole-cell and acellular pertussis vaccines in children, finding that all tested vaccines are effective, with whole-cell vaccines showing variable efficacy and a higher incidence of adverse events compared to acellular v…
DOI: 10.1016/s0264-410x(02)00770-3 -
Cutaneous Adverse Events After COVID-19 Vaccination
This study investigates the incidence and characteristics of cutaneous adverse reactions (CARs) following COVID-19 vaccination in Thailand, finding a low overall incidence of 1.2% with underlying urticaria and psoriasis as significant risk factors.
DOI: 10.2147/CCID.S410690 -
U.S. Population-Based background incidence rates of medical conditions for use in safety assessment of COVID-19 vaccines
Comprehensive compilation and synthesis of US background incidence rates for medical conditions that are potential adverse events of special interest in vaccine safety surveillance, with by-age/sex/race breakdowns where available, to aid contextualization of COVID-19 vaccine saf…
DOI: 10.1016/j.vaccine.2021.05.016 -
Primary Immunization of Premature Infants with Gestational Age <35 Weeks: Cardiorespiratory Complications and C-Reactive Protein Responses Associated with Administration of Single and Multiple Separate Vaccines Simultaneously
This study investigates the incidence of cardiorespiratory events and abnormal C-reactive protein (CRP) levels in premature infants receiving single versus multiple vaccines simultaneously, finding a higher incidence of adverse events associated with multiple vaccinations.
DOI: 10.1016/j.jpeds.2007.02.059 -
Myocarditis and Pericarditis following COVID-19 Vaccination in Thailand
This study investigates the incidence and characteristics of myocarditis and pericarditis following COVID-19 vaccination in Thailand, revealing a higher incidence among male adolescents, particularly after mRNA vaccinations, while emphasizing the overall mild nature of these adv…
DOI: 10.3390/vaccines11040749 -
Adverse Events Following Pneumococcal Vaccination among Infants attending Immunization Clinic at a Tertiary Hospital in Northern India
A prospective active-surveillance study at a North Indian tertiary hospital assessing the incidence and determinants of adverse events following pneumococcal vaccination (PCV-13) in infants, finding mostly mild AEFIs, higher incidence after the first two doses and no serious eve…
DOI: 10.47203/ijch.2020.v32i03.018 -
NEURO-COVAX: An Italian Population-Based Study of Neurological Complications after COVID-19 Vaccinations
This study evaluates the neurological complications following COVID-19 vaccinations in an Italian population, revealing a significant incidence of adverse neurological events, particularly associated with the ChAdOx1nCov-19 vaccine.
DOI: 10.3390/vaccines11101621 -
Vaccine adverse events reported in post-marketing study of the Kitasato Institute from 1994 to 2004
This study analyzes vaccine adverse events reported in Japan from 1994 to 2004, categorizing them into allergic reactions and severe systemic illnesses, and highlights the low incidence of serious adverse events associated with vaccination.
DOI: 10.1016/j.vaccine.2006.05.130 -
Headache onset after vaccination against SARS-CoV-2: a systematic literature review and meta-analysis
This systematic literature review and meta-analysis investigates the incidence and characteristics of headache as an adverse event following vaccination against SARS-CoV-2, revealing that 22% of subjects experienced headache after the first dose and 29% after the second, with no…
DOI: 10.1186/s10194-022-01400-4 -
How Safe Are COVID-19 Vaccines in Individuals with Immune-Mediated Inflammatory Diseases? The SUCCEED Study
The SUCCEED study investigates the safety of COVID-19 vaccines in individuals with immune-mediated inflammatory diseases, finding a low incidence of serious adverse events within 31 days post-vaccination.
DOI: 10.3390/vaccines12091027 -
Adverse events of special interest after vaccination with COVID-19 vaccines: a cohort event monitoring study in Iran
A WHO-guided cohort event monitoring study in Iran assessing adverse events of special interest (AESIs) and serious adverse events (SAEs) after four COVID-19 vaccines (Sinopharm, Sputnik V, AZD1222, and COVIran Barekat) in 89,783 adults across seven cities, finding very rare AES…
DOI: 10.1186/s40001-025-03015-2 -
Case of Myocarditis, Pericarditis, and Fatal Aortic Dissection Following COVID-19 mRNA Vaccination
A 34-year-old previously healthy male developed myocarditis, pericarditis, and a fatal thoracic aortic dissection 16 days after his first COVID-19 mRNA vaccine dose, with autopsy showing vaccine-derived spike protein and eosinophilic/lymphocytic infiltrates.
DOI: 10.33140/bscr.03.03.03 -
Acute myocarditis caused by COVID-19 disease and following COVID-19 vaccination
This narrative review summarizes evidence that COVID-19 and mRNA COVID-19 vaccination can cause rare myocarditis, most common in younger males after second dose, with favourable short-term course and benefit-risk favouring vaccination.
DOI: 10.1136/openhrt-2021-001957 -
Myocarditis after COVID-19 mRNA vaccination: clinical observations and potential mechanisms
This study examines the incidence and implications of acute myocarditis associated with COVID-19 mRNA vaccination compared to myocarditis resulting from COVID-19 infection, highlighting the rarity of vaccine-related myocarditis and the greater risks associated with COVID-19 itse…
DOI: 10.1038/s41569-021-00662-w -
Myocarditis after COVID-19: Comparing risks from vaccination and infection
A meta-analysis and FDA reports show COVID-19 infection carries a higher risk of myocarditis and more severe outcomes than mRNA vaccination, so vaccine benefits outweigh risks.
DOI: 10.47391/jpma.32162 -
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 -
COVID-19 and Myocarditis: Review of Clinical Presentations, Pathogenesis and Management
A comprehensive review of how COVID-19, MIS, post-acute COVID-19 syndrome, and vaccination relate to myocarditis, summarizing clinical presentations, proposed pathogenesis, diagnostic approaches, and current management with discussion of limitations and gaps for future research.
DOI: 10.17925/hi.2022.16.1.20 -
Self-limited myocarditis presenting with chest pain and ST segment elevation in adolescents after vaccination with the BNT162b2 mRNA vaccine
Two adolescents developed self-limited myocarditis with chest pain, elevated troponin, ST segment elevation, and cardiac MRI enhancement within 3 days of BNT162b2 vaccination, suggesting a possible vaccine-associated adverse event.
DOI: 10.1017/s1047951121002547 -
Vaccine-associated hypersensitivity
This study reviews vaccine-associated hypersensitivity reactions, highlighting their rarity, the components involved, and the need for further research on the pathophysiology and risk factors associated with these reactions.
DOI: 10.1016/j.jaci.2017.12.971 -
Who Is Really at Risk for Anaphylaxis Due to COVID-19 Vaccine?
An expert commentary reviews early anaphylaxis reports after Pfizer-BioNTech COVID-19 vaccination and proposes a pragmatic risk-stratification protocol, arguing the MHRA's broad contraindication is overly restrictive.
DOI: 10.3390/vaccines9010038 -
Safety and efficacy of venom immunotherapy: a real life study
Retrospective real-life study evaluating safety, efficacy, and adherence of venom immunotherapy in 180 adults with Hymenoptera venom allergy, finding VIT highly effective with more adverse events in bee venom, and identifying beekeeping and female sex as risk factors.
DOI: 10.5114/ada.2017.67082 -
Mecanismo y diseño de vacunas para el sars-cov-2, revisión narrativa
This narrative review describes SARS-CoV-2 vaccine mechanisms and designs, reporting that mRNA vaccines (BNT162b2 and mRNA-1273) demonstrate the highest efficacy (93-95%), adenovirus vector vaccines show 66.9-91.6% efficacy, and inactivated CoronaVac shows 83.5%, with rare safet…
DOI: 10.18566/medupb.v43n1.a10