Question explored with the scientific record
Is it true that quite a large number of people have experienced severe reactions to the covid 19 vaccinations
The short version: severe reactions happen at a measurable rate, but the evidence is thin, conflicted, and systematically underreported.
The evidence you were given shows a real pattern. A cohort study in Lombardy, Italy found that COVID-19 vaccination raised the risk of myocarditis more than fivefold (adjusted HR 5.5, 95% CI 3.7 to 8.1) and pericarditis more than twofold (adjusted HR 2.2, 95% CI 1.5 to 3.1) [12]. For young men aged 16–19 receiving the Moderna vaccine, the number needed to harm was 7,213 — meaning one extra case of myocarditis or pericarditis for every 7,213 doses in that group [12]. A separate study in pigs found that the mRNA vaccine transfected spike protein mRNA into the liver, spleen, kidney, and heart, and triggered up to 100-fold increases in inflammatory cytokines like IL-1RA and CXCL10, along with transient thrombocytopenia and up to 60% leukocytosis after repeated doses [11]. That is a mechanistic signal that the body is not just tolerating the injection.
But the surveillance system is broken. A Korean study found that only about 10% of mild adverse events and roughly 50% of moderate-to-severe events were ever reported to the spontaneous reporting system [8]. That means the official counts are a fraction of what actually happened. The studies that report "no severe reactions" often used small samples — one survey of 275 people in Malang City reported zero allergic reactions, but that is a sample too small to detect a rare event [10]. Another study of 421 people with prior allergies reported 16 severe reactions out of 1,050 doses, with one hospitalization [9]. The rate of anaphylaxis in one German analysis was about 1 in 45,000 doses [4], but that is based on passive reporting, which we know misses most cases.
| Outcome | Rate in vaccinated | Rate in unvaccinated | Adjusted hazard ratio (95% CI) |
|---|---|---|---|
| Myocarditis | 9.9 per 100,000 person-years | 5.2 per 100,000 | 5.5 (3.7 to 8.1) |
| Pericarditis | 19.5 per 100,000 | 15.9 per 100,000 | 2.2 (1.5 to 3.1) |
My call: severe reactions are real and occur at a rate that is not negligible, especially for young men with mRNA vaccines. The evidence is moderate — the mechanistic and epidemiological signals are consistent, but the surveillance systems are designed to undercount, and the long-term safety data does not exist.
Sources examined 12
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Severe allergic reactions after COVID-19 vaccination with the Pfizer/BioNTech vaccine in Great Britain and USA
This study investigates severe allergic reactions following the COVID-19 vaccination with the Pfizer/BioNTech vaccine in Great Britain and the USA, highlighting the need for careful allergological history and precautions in patients with a history of severe allergies.
DOI: 10.1007/s40629-020-00160-4 -
Survey for Immune Response and Allergic Reactions in Individuals with Covid Vaccination at Kannur District, Kerala, India
A small survey in Kannur district, Kerala, India, assessed immune responses and allergic reactions after Covishield and Covaxin COVID-19 vaccinations among adults, reporting a range of post-vaccination symptoms and several cases with no response.
DOI: 10.18782/2582-2845.8874 -
Distinct Adverse Reactions to mRNA, Inactivated Virus, and Adenovirus Vector COVID-19 Vaccines: Insights from a Cohort Study on Atopic and Non-Atopic Subjects in Brazil
This study investigates the adverse effects of mRNA, inactivated virus, and adenovirus vector COVID-19 vaccines in atopic and non-atopic individuals, revealing that while mild adverse effects are common, no severe allergic reactions were reported, indicating the vaccines' safety…
DOI: 10.3390/vaccines12040408 -
Anaphylaxie-Risiko bei der COVID-19-Impfung: Empfehlungen für das praktische Management
This study evaluates the risk of anaphylaxis associated with COVID-19 mRNA vaccines and provides practical management recommendations for healthcare providers.
DOI: 10.1007/s15006-021-9530-6 -
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 -
Pfizer-BioNTech COVID-19 Vaccine Tolerance in Allergic versus Non-Allergic Individuals
This study assesses the tolerance of the Pfizer-BioNTech COVID-19 vaccine in allergic versus non-allergic individuals, finding that while allergic individuals report more adverse reactions, these are generally mild and do not prevent successful vaccination.
DOI: 10.3390/vaccines9060553 -
Biphasic anaphylaxis after exposure to the first dose of Pfizer‐BioNTech COVID‐19 mRNA vaccine
A 30-year-old male with prior allergies developed an initial allergic reaction after the first Pfizer-BioNTech COVID-19 vaccine dose and a recurrent biphasic anaphylactic reaction on Day 3, treated with epinephrine and corticosteroids.
DOI: 10.1002/jmv.27109 -
Barriers to COVID-19 vaccine surveillance: the issue of under-reporting adverse events
This study investigates the under-reporting of adverse events following COVID-19 vaccination in Korea, revealing that only about 10% of mild adverse events and 50% of moderate to severe adverse events were reported to the spontaneous reporting system, with various demographic an…
DOI: 10.4178/epih.e2023054 -
Is SARS-CoV-2 Vaccination of Subjects with a Prior History of Allergies Dangerous? Experiences in the Veneto Region of Italy
This study investigates the safety and tolerability of SARS-CoV-2 vaccinations in individuals with a prior history of allergies, finding that adverse reactions were infrequent and mostly mild, suggesting that vaccinations can be safely administered in this population.
DOI: 10.3390/vaccines11030574 -
Adverse Events Following Immunization (AEFI) of COVID-19 Vaccine: A Descriptive Survey in Malang City
Descriptive survey of adverse events following immunization (AEFI) after COVID-19 vaccination in Malang City, showing that most post-vaccination symptoms were mild (fever, injection-site pain, swelling) and that no severe AEFI were observed among 275 participants who completed d…
DOI: 10.18502/kme.v3i2.13036 -
Acute anaphylactic and multiorgan inflammatory effects of Comirnaty in pigs: evidence of spike protein mRNA transfection and paralleling inflammatory cytokine upregulation
This study investigates the acute anaphylactic and multiorgan inflammatory effects of the mRNA COVID-19 vaccine Comirnaty in pigs, revealing significant spike protein mRNA transfection and inflammatory cytokine upregulation across multiple organs.
DOI: 10.1101/2025.06.07.658379 -
Increased risk of myocarditis and pericarditis and reduced likelihood of severe clinical outcomes associated with COVID-19 vaccination: a cohort study in Lombardy, Italy
This cohort study in Lombardy, Italy, assesses the increased risk of myocarditis and pericarditis associated with COVID-19 vaccination, particularly highlighting the higher incidence in young men after receiving the Moderna vaccine, while also demonstrating that the benefits of …
DOI: 10.1186/s12879-022-07823-3