Question explored with the scientific record
I'd like to know about the Pfeizer Covid vaccine and whether it has caused breast cancer and/or chronic spontaneous urticaria
The short version: the retrieved evidence does not contain a single study that directly tests whether the Pfizer mRNA vaccine causes breast cancer or chronic spontaneous urticaria in the general population.
The evidence you gave me is almost entirely off-topic. It covers transplant recipients [1], mice [2, 9], infants [3], heart failure patients [6], and rare case reports of thyroiditis [5], vasculitis [7], myocarditis [11], cutaneous lymphoma [12], and immune thrombocytopenia [14]. None of these studies were designed to answer your question. A case report of a 75-year-old woman whose pre-existing mycosis fungoides progressed after vaccination [12] is not evidence that the vaccine causes breast cancer. A case of cutaneous vasculitis [7] is not chronic spontaneous urticaria. The study on vaccine mRNA persistence in cardiac tissue [4] does not address breast tissue or chronic hives.
The absence of direct evidence is itself the finding. No large, long-term, controlled study comparing breast cancer or chronic urticaria rates in vaccinated versus unvaccinated women appears in this evidence set. The most informative study design, a prospective cohort with a true unvaccinated control group tracking these specific outcomes over years, was not provided. The burden of proof is on the intervention, and the evidence retrieved does not meet it for either condition.
My call: the evidence retrieved does not support a causal link between the Pfizer mRNA vaccine and breast cancer or chronic spontaneous urticaria, but it also does not rule one out because the relevant studies were never presented. Confidence: low, due to the complete absence of directly applicable evidence.
Sources examined 14
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Leukocyte Count in Solid Organ Transplant Recipients After SARS-CoV-2 mRNA Vaccination and Infection
This study investigates the impact of SARS-CoV-2 mRNA vaccination and infection on leukocyte counts in solid organ transplant recipients, finding no association between vaccination and decreased leukocyte counts, while infection significantly increased the risk of leukopenia.
DOI: 10.3390/vaccines13020103 -
Memory B cell Development in Response to mRNA SARS-CoV-2 and Nanoparticle Immunization in Mice
Memory B cell and serologic responses to SARS-CoV-2 mRNA vaccination, beta nanoparticle, and mosaic 8b nanoparticle immunogens were compared in mice, revealing that nanoparticle vaccines broaden memory B cell antibody breadth and epitopic targeting compared with mRNA, while mRNA…
DOI: 10.1101/2025.10.01.679787 -
Infant CD4 T-cell response to SARS-CoV-2 mRNA vaccination is restricted in cytokine production and modified by vaccine manufacturer
This study investigates the CD4 T-cell response to SARS-CoV-2 mRNA vaccination in infants, revealing restricted cytokine production compared to adults and variations based on the vaccine manufacturer.
DOI: 10.1101/2025.04.02.646864 -
Duration of SARS-CoV-2 mRNA vaccine persistence and factors associated with cardiac involvement in recently vaccinated patients
This autopsy-based study maps the tissue distribution and persistence of SARS-CoV-2 mRNA vaccines in recently vaccinated humans, finding vaccine mRNA in axillary lymph nodes within 30 days and in a subset of cardiac tissue associated with healing myocardial injury, while liver a…
DOI: 10.1038/s41541-023-00742-7 -
LBSAT312 SARS-CoV-2 MRNA Vaccine Side Effects Or Something More? Case Series - Vaccine Induced Mild, Self-limiting Thyroiditis.
Two healthy women developed transient, self-limiting thyroiditis with suppressed TSH and elevated free T4 within weeks of SARS-CoV-2 mRNA vaccination, followed by resolution with conservative management.
DOI: 10.1210/jendso/bvac150.1544 -
Risk of worsening heart failure and all-cause mortality following mRNA COVID-19 vaccination in patients with heart failure: a Danish nationwide real-world safety study
In a nationwide Danish cohort of 101,786 patients with heart failure, SARS-CoV-2 mRNA vaccination was associated with a lower 90-day all-cause mortality risk compared with a matched 2019 unvaccinated cohort and with no difference in worsening heart failure, myocarditis, or venou…
DOI: 10.1093/eurheartj/ehac544.881 -
SARS-COV-2 MRNA vaccine-associated cutaneous vasculitis
This case report describes a 38-year-old male who developed cutaneous vasculitis four days after receiving the SARS-CoV-2 mRNA vaccine, which was successfully treated with medium-dose methylprednisolone.
DOI: 10.14744/nci.2022.22309 -
Spotlight on Neutralizing Antibodies of Mrna-1273 and BNT162b2 Mrna Vaccines against SARS-Cov 2 Omicron
This narrative review discusses the immune responses to SARS-CoV-2 mRNA vaccines (mRNA-1273 and BNT162b2), their mechanisms, the impact of the Omicron variant, and future strategies such as booster shots and updated vaccines.
DOI: 10.55529/jcpp.35.38.46 -
Memory B cell development in response to mRNA SARS-CoV-2 and nanoparticle immunization in mice
Mosaic 8b RBD nanoparticle vaccines broaden memory B cell antibody breadth against diverse sarbecoviruses in mice, while SARS-CoV-2 mRNA vaccination yields higher serum neutralizing titers against the cognate antigen.
DOI: 10.1073/pnas.2527869123 -
Immune response to SARS-CoV-2 mRNA vaccination and booster dose in patients with multiple myeloma and monoclonal gammopathies: impact of Omicron variant on the humoral response
This study assesses both humoral and cellular immune responses to two-dose mRNA SARS-CoV-2 vaccination and a heterologous booster in patients with MGUS, SMM, and multiple myeloma (newly diagnosed and relapsed/refractory), revealing impaired responses in MM—especially relapsed/re…
DOI: 10.1080/2162402X.2022.2120275 -
Case report: acute myocarditis following the second dose of mRNA-1273 SARS-CoV-2 vaccine
A 44-year-old man developed acute myocarditis four days after the second dose of the mRNA-1273 SARS-CoV-2 vaccine, with cardiac MRI findings compatible with myocarditis, and his symptoms and ejection fraction normalized at one-month follow-up.
DOI: 10.1093/ehjcr/ytab319 -
Rapid Progression of Cutaneous Lymphoma Following mRNA COVID-19 Vaccination: A Case Report and Pathogenetic Insights
This case report documents the development and rapid progression of mycosis fungoides following SARS-CoV-2 mRNA vaccination (Pfizer-BioNTech), discusses potential immunomodulatory mechanisms, and reviews related literature to raise awareness of rare vaccine-associated cutaneous …
DOI: 10.3390/vaccines13070678 -
Approximative He Hamiltonian in descriptive multidimensional scaling statistics of RNA contained information with application to SARS-CoV-2 Spike mRNA and 7SLRNA, RN7SL2 and RN7SL3
An in silico study using multidimensional scaling and a He-like Hamiltonian to compare SARS-CoV-2 Spike mRNA subsequences with 7SL RNA (and related RN7SL RNAs) to identify regions that resemble 7SL RNA and discuss whether such regions could behave like Alu-like parasitic DNA via…
DOI: 10.1016/j.genrep.2021.101203 -
Severe immune thrombocytopenia (ITP) following SARS-CoV-2 mRNA vaccine in a girl on immunosuppressive treatment and in prolonged stable phase of ITP.
Case report of a young woman with chronic immune thrombocytopenia who developed a severe relapse 15 days after the second Pfizer-BioNTech SARS-CoV-2 vaccine while on mycophenolate, successfully treated with IVIG and prednisone, with concurrent institutional observation of vaccin…
DOI: 10.4084/mjhid.2022.011