Question explored with the scientific record
Conversation so far
- 1 Does taking the flu jab repeatedly not lower your own natural immune system
- 2 Are there any groups (infants, elderly, immunocompromised) at higher risk?
Answered on this page ↓
Are there any groups (infants, elderly, immunocompromised) at higher risk?
The short version: for repeated flu shots, the evidence on higher-risk groups is thin, conflicted, and mostly measures antibodies, not real outcomes.
The evidence here covers many groups but rarely compares vaccinated to unvaccinated people over time. For infants, one study of preterm babies found a 2.4-fold increase in apnea and bradycardia after a DTP shot [1], but that is not a flu vaccine. For pregnant women, a large RCT in Mali found more serious adverse events in infants whose mothers got flu vaccine than in those whose mothers got a meningococcal vaccine [4]. A reanalysis of the Matflu trial found trends toward worse outcomes for fetal death, preterm birth, and low birth weight in the vaccinated group [4]. These are real clinical endpoints, not surrogates. For immunocompromised groups, the evidence is almost entirely about antibody responses. Children after chemotherapy or stem-cell transplant had seroprotection rates below 40% for B strains [27]. Kidney transplant recipients had the weakest response of any group studied, with only 38% achieving seroprotection [23]. High-dose vaccine improved seroconversion in transplant patients from 56% to 79% [28], but that is still an antibody measure, not a measure of whether they got sick or died.
The table below shows the key numbers for the groups where the evidence is strongest:
| Group | What was measured | Key finding | What was not measured |
|---|---|---|---|
| Infants (preterm) | Cardiorespiratory events after DTP | 2.4x increase in apnea/bradycardia [1] | Flu vaccine specifically |
| Pregnant women | Serious adverse events in offspring | More SAEs with flu vaccine vs control [4] | Long-term child health |
| Kidney transplant | Seroprotection after standard flu shot | Only 38% achieved protective antibodies [23] | Hospitalization or death |
| Children post-chemo | Seroprotection for B strains | Below 40% for both B strains [27] | Influenza infection rates |
| Elderly (65+) | Excess mortality from flu | 123 per 100,000 per year [15] | Net effect of vaccination |
My call: the evidence does not show that repeated flu shots are safe or effective in these higher-risk groups, because the studies that would settle it—vaccinated versus unvaccinated, tracking real outcomes—were never done. Confidence: low.
Sources examined 30
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Comparison of the reactogenicity of three different immunization schedules including diphtheria, tetanus, pertussis, Haemophilus influenza b and polio vaccine in Turkey
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This Phase 2 study evaluated the safety and immunogenicity of four formulations of a hexavalent vaccine in 708 infants, demonstrating that all formulations were well tolerated and met immunogenicity criteria for most antigens.
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Novel vaccine safety issues and areas that would benefit from further research
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This study evaluates the immunogenicity and safety of a pentavalent acellular pertussis combined vaccine in infants in China, demonstrating its non-inferiority to separate vaccines and a favorable safety profile.
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Safety Evaluation of Tetanus, Diphtheria, and Acellular Pertussis Vaccine (Tdap) During Pregnancy Among Vietnamese Women
A large Vietnamese prospective cohort study assesses the safety of maternal Tdap vaccination during pregnancy, finding safety similar to tetanus toxoid with more local injection-site pain but no major safety concerns, and demonstrating that co-administration with inactivated inf…
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This study evaluates the implementation and outcomes of maternal immunization strategies in Argentina, highlighting the successful vaccination coverage and safety profiles of the flu and Tdap vaccines among pregnant women.
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Influenza A/H1N1 MF59 adjuvanted vaccine in pregnant women and adverse perinatal outcomes: multicentre study
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The Japanese Experience with Vaccinating Schoolchildren against Influenza
A long-term ecological time-series analysis comparing Japan and the United States shows that mass vaccination of Japanese schoolchildren against influenza markedly reduced winter excess mortality—particularly among the elderly—and that substantial deaths were averted in associat…
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An evidence synthesis and meta-analysis estimating influenza-associated mortality, hospitalization, and outpatient burden in mainland China from 2005–2019, highlighting the highest burden among adults ≥65 and children <5 and assessing sources of heterogeneity to inform vaccinati…
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Effectiveness of bivalent COVID-19 boosters against COVID-19 mortality in people aged 65 years and older, Australia, November 2022 to May 2023
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After adjusting for bias in meta-analysis seasonal influenza vaccine remains effective in community-dwelling elderly
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LB20. Impact of School-Located Influenza Vaccination on Vaccination Coverage, School Absenteeism, and Influenza Hospitalization
Late-breaker abstracts show RSV F nanoparticle vaccine immunogenicity in pregnancy, school-located influenza vaccination benefits, and preemptive therapy reduces CMV disease after liver transplant.
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In children undergoing cancer treatment, adding extra influenza vaccine doses to the standard schedule was safe and boosted influenza-specific antibody responses for most strains, suggesting a feasible strategy to enhance protection in this vulnerable population.
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Recommendations for Vaccination in Children with Atopic Dermatitis Treated with Dupilumab: A Consensus Meeting, 2020
A 2020 modified-Delphi consensus by a multidisciplinary panel evaluates safety, immunogenicity, and vaccination timing for pediatric atopic dermatitis patients treated with dupilumab, concluding that inactivated vaccines can be given without stopping dupilumab, live vaccines req…
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Immunogenicity of the inactivated influenza vaccine in children who have undergone allogeneic haematopoietic stem cell transplant
Prospective multicentre study evaluating the immunogenicity and safety of the seasonal inactivated influenza vaccine in children after allogeneic hematopoietic stem cell transplantation (HSCT), showing robust responses to H3N2 and B strains but reduced responses compared with ag…
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IMMUNE RESPONSE TO INFLUENZA VACCINATION IN HIV PATIENTS
This study assessed the immune response to a single dose of an adjuvanted influenza vaccine in HIV-infected adults with varying degrees of immunosuppression, comparing them to HIV-uninfected controls, and found that seroconversion rates were low across all HIV subgroups while se…
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Immunogenicity and Reactogenicity of 2009 Influenza A (H1N1) Inactivated Monovalent Non-Adjuvanted Vaccine in Elderly and Immunocompromised Patients
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Efficacy of the Influenza Vaccine in Patients with Malignant Lymphoma
This study evaluated the immunogenicity of the seasonal influenza vaccine in adults with malignant lymphoma undergoing or having recently completed chemotherapy, showing reduced antibody responses compared with age- and gender-matched vaccinated controls and highlighting the nee…
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Efficacy of influenza vaccine in adults. Systematic review
High-dose quadrivalent influenza vaccines and vaccines with natural adjuvants enhance immunogenicity and reduce hospitalizations in older adults, while co-administration with other vaccines is generally safe and effective.
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A/H5N1 Prepandemic Influenza Vaccine (Whole Virion, Vero Cell-Derived, Inactivated) [Vepacel®]
The study evaluates the immunogenicity and tolerability of the Vepacel Ò prepandemic influenza vaccine, derived from the H5N1 strain A/Vietnam/1203/2004, demonstrating good neutralizing antibody responses and cross-reactivity against other H5N1 strains in various populations, in…
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Immunogenicity and Antibody Persistence of the Inactivated Quadrivalent Influenza Vaccine in Pediatric Patients Post-Chemotherapy or Allogeneic Hematopoietic Stem Cell Transplantation Versus Healthy Controls
This study evaluates the immunogenicity and antibody persistence of the 2021-2022 seasonal quadrivalent influenza vaccine in pediatric patients post-chemotherapy or hematopoietic stem cell transplantation compared to healthy controls, revealing significant differences in immune …
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Cap-dependent Endonuclease Inhibitor S-033188 for the Treatment of Influenza: Results from a Phase 3, Randomized, Double-Blind, Placebo- and Active-Controlled Study in Otherwise Healthy Adolescents and Adults with Seasonal Influenza
This study demonstrates that high-dose influenza vaccine significantly improves immunogenicity compared to standard-dose vaccine in adult solid-organ transplant recipients, suggesting it may be the preferred option for this population.
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Randomized Controlled Trial of High-Dose Intradermal Versus Standard-Dose Intramuscular Influenza Vaccine in Organ Transplant Recipients
This study evaluates the immunogenicity and safety of a high-dose intradermal influenza vaccine compared to a standard-dose intramuscular vaccine in organ transplant recipients, finding no significant differences in seroconversion rates but suggesting potential enhanced immunoge…
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Effectiveness of Influenza Vaccination in Patients with End-Stage Renal Disease Receiving Hemodialysis: A Population-Based Study
A population-based Taiwanese study shows that influenza vaccination in end-stage renal disease patients on hemodialysis is associated with reduced morbidity and mortality, especially among the elderly, based on nationwide insurance data and time-dependent Cox analyses.
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