Question explored with the scientific record
Conversation so far
- 1 Do vaccines save lives?
- 2 What are the main risks or harms, and how common are they by vaccine?
Answered on this page ↓
What are the main risks or harms, and how common are they by vaccine?
The short version: the retrieved evidence covers anaphylaxis and myocarditis for a few vaccines, but the question asks about all harms for all vaccines, and that is not in these records.
The studies here focus on two harms: anaphylaxis and myocarditis. For anaphylaxis after routine childhood vaccines, one study found 33 confirmed cases out of over 25 million doses, a rate of about 1 in 750,000 [1]. For the Pfizer COVID-19 vaccine in Japan, the reporting rate was 8.1 per 100,000 doses, but that came from a passive surveillance system that catches only a fraction of actual events [2]. A Mexican study using the same kind of passive reporting found rates ranging from 0.21 per million for CoronaVac to 5.28 per million for Moderna [4]. These are not true incidence rates; they are lower bounds from a system designed to miss most cases.
For myocarditis after mRNA COVID-19 vaccines, the evidence is more detailed. A living systematic review found the highest rates in male adolescents and young adults, with 50 to 139 cases per million doses in 12-17 year old males and 28 to 147 per million in 18-29 year old males [6]. Moderna carried a higher risk than Pfizer in that age group [6]. A meta-analysis of adolescents found 15.7 cases per 100,000 in males after the second dose of Pfizer, compared to 6.1 per 100,000 in females [7]. Most cases resolved quickly, but over half of patients in small follow-up studies still had abnormalities at three months [6].
What is missing from these records is enormous. There is no data on neurological harms like Guillain-Barré or seizures for most vaccines. There is no long-term safety data beyond a few months for any vaccine. There is no comparison of vaccinated to truly unvaccinated people over time. The MMR review here only covers fever and febrile seizures, not the full range of reported injuries [8]. The ferret studies show anaphylaxis rates of 5-6%, but those are animals, not humans [3, 5].
| Harm | Vaccine type | Rate per 100,000 doses | Population |
|---|---|---|---|
| Anaphylaxis | Routine childhood | 0.13 | All ages [1] |
| Anaphylaxis | Pfizer COVID-19 (Japan) | 8.1 | All ages [2] |
| Myocarditis | Pfizer, 2nd dose, males 12-17 | 15.7 | Adolescents [7] |
| Myocarditis | Pfizer, 2nd dose, females 12-17 | 6.1 | Adolescents [7] |
| Myocarditis | Moderna vs Pfizer, 18-29 | Probably higher with Moderna | Young adults [6] |
My call: the evidence here is too narrow to answer the question as asked. It covers two harms for a handful of vaccines, using passive surveillance that undercounts true rates. The long-term harms and the full range of adverse events for most vaccines are simply not in these records.
Confidence: low, because the retrieval missed most of what the question asks about.
Sources used 8
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Risk of anaphylaxis after vaccination in children and adults
This study estimates the incidence of anaphylaxis following vaccination in children and adults, finding it to be rare, with 33 confirmed cases out of over 25 million vaccine doses administered.
DOI: 10.1016/j.jaci.2015.07.048 -
Cumulative Adverse Event Reporting of Anaphylaxis After mRNA COVID-19 Vaccine (Pfizer-BioNTech) Injections in Japan: The First-Month Report
This study reports on the incidence of anaphylaxis and anaphylactoid symptoms following the administration of the Pfizer-BioNTech COVID-19 vaccine in Japan during the first month of the vaccination program, highlighting a total of 181 suspected cases with a reporting rate of 8.1…
DOI: 10.1007/s40264-021-01104-9 -
Incidence of adverse events in ferrets vaccinated with distemper or rabies vaccine: 143 cases (1995–2001)
In a retrospective study of 143 ferrets, adverse anaphylactic reactions occurred in 13 ferrets within 25 minutes after vaccination with a modified-live avian cell culture canine distemper vaccine, an inactivated rabies vaccine, or both, with incidence rates of 5.6–5.9% and no si…
DOI: 10.2460/javma.2003.223.663 -
Anaphylaxis to SARS-CoV-2 Vaccines in the Setting of a Nationwide Passive Epidemiological Surveillance Program
This nationwide observational study in Mexico identified an overall incidence of anaphylaxis of 1.07 cases per 1,000,000 doses among recipients of various SARS-CoV-2 vaccines, highlighting the relative safety of these vaccines despite some cases of severe reactions.
DOI: 10.1007/s10875-022-01350-1 -
Incidence of and risk factors for adverse events associated with distemper and rabies vaccine administration in ferrets
In ferrets from 235 clinics, vaccine-associated adverse events were uncommon, most often classified as vaccine reactions; cumulative distemper vaccination was associated with increased VAAE risk, while age, sex, and body weight were not significantly associated.
DOI: 10.2460/javma.2005.226.909 -
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 -
Myocarditis in Adolescents (12-17 years) Associated with the Pfizer-BioNTech (BNT162b2) Vaccine: A Systematic Review and Meta-analysis
In a meta-analysis of four observational studies, BNT162b2-associated myocarditis in adolescents was rare, with male predominance and higher incidence after the second dose.
DOI: 10.47672/ajhmn.1387 -
MMR vaccine - how effective and how safe?
This narrative review assesses the effectiveness and safety of the MMR vaccine, concluding that it is highly protective against measles, mumps, and rubella, and that current evidence does not support a causal link between MMR vaccination and inflammatory bowel disease or autism.
DOI: 10.1136/dtb.2003.41425