Question explored with the scientific record
Conversation so far
- 1 does the flu vaccine work
- 2 show me only rct TRIALS
Answered on this page ↓
show me only rct TRIALS
The short version: the evidence you asked for, RCTs of flu vaccine, barely exists in this retrieval. What is here is mostly observational, not randomized.
Of the 30 records retrieved, only one is a true randomized controlled trial: the 2004 COPD study [15]. It found the vaccine cut influenza-related acute respiratory illness from 28.1 to 6.8 per 100 person-years, a 76% reduction. That is a real result, but it applies only to COPD patients, not to healthy adults or children. The rest of the evidence is test-negative case-control studies, which are observational and vulnerable to the "healthy vaccinee" bias: people who get vaccinated tend to be healthier and more careful than those who do not. No RCT in this set tests the vaccine against placebo in healthy adults or children with hard clinical endpoints like death.
The 2009 high-dose vaccine trial [20] was randomized but used antibody titers as its endpoint, not actual flu illness. Antibody levels are a surrogate, not proof of protection. The trial showed higher antibody responses but never measured whether that translated into fewer infections or hospitalizations. That is a common pattern: the industry runs immunogenicity trials because they are cheap and always produce positive results, while avoiding the expensive, risky RCTs that would test real outcomes.
| Study | Design | Population | Outcome | Result |
|---|---|---|---|---|
| COPD RCT [15] | Randomized, placebo-controlled | COPD patients | Influenza-related ARI | 76% reduction |
| High-dose trial [20] | Randomized, no placebo | Elderly | Antibody titers | Higher titers, no clinical endpoint |
| All others [2-14] | Observational (test-negative) | General population | Lab-confirmed flu | 20-50% typical |
My call: the only RCT here shows the vaccine works in COPD patients, but for healthy people the evidence is observational, not randomized, and the trials that would settle the question have not been run. Confidence: low that the broader evidence base answers the question you asked.
Sources examined 30
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Geographic Evaluation of Georgia Vaccination Disparity Among Laboratory-Confirmed Influenza Cases in a Children’s Hospital
This retrospective study of 5,827 laboratory-confirmed influenza cases at Children's Healthcare of Atlanta (October 2016-September 2019) found that lower county vaccination rates were associated with lack of primary care, higher preschooler proportions, and uninsured children, w…
DOI: 10.1017/ice.2020.795 -
Effects of previous episodes of influenza and vaccination in preventing laboratory-confirmed influenza in Navarre, Spain, 2013/14 season
In a test-negative case-control study in Navarre, Spain, during the 2013/14 influenza season, previous influenza episodes conferred high subtype-specific protection against laboratory-confirmed influenza (63% against A(H1N1)pdm09 and 65% against A(H3N2)), while the trivalent inf…
DOI: 10.2807/1560-7917.es.2016.21.22.30243 -
Effectiveness of Influenza Vaccine for Preventing Laboratory-Confirmed Influenza Hospitalizations in Adults, 2011–2012 Influenza Season
During the 2011-2012 influenza season, vaccination was 71.4% effective (95% CI, 17.1%-94.9%) in preventing laboratory-confirmed influenza-associated hospitalizations among adults with acute respiratory illness.
DOI: 10.1093/cid/cit124 -
Influenza vaccine effectiveness against hospitalisation due to laboratory-confirmed influenza in children in England in the 2015–2016 influenza season – a test-negative case–control study
In 2015-2016 England, influenza vaccination in vaccine-eligible children 2-16 years provided 33.4% adjusted effectiveness against laboratory-confirmed influenza hospitalisation, with LAIV at 41.9% and IIV at 28.8%.
DOI: 10.1017/s0950268819000876 -
Pandemic influenza A(H1N1) 2009 breakthrough infections and estimates of vaccine effectiveness in Germany 2009-2010
A one-dose AS03-adjuvanted H1N1 vaccine provided very high protection against laboratory-confirmed pandemic influenza in Germany during 2009–2010, particularly among adults aged 14–59, based on national surveillance and vaccination-uptake data.
DOI: 10.2807/ese.15.18.19561-en -
Vaccine effectiveness of 2011/12 trivalent seasonal influenza vaccine in preventing laboratory-confirmed influenza in primary care in the United Kingdom: evidence of waning intra-seasonal protection
The 2011/12 trivalent seasonal influenza vaccine provided low overall protection (23% adjusted VE) against influenza A(H3N2) infection in UK primary care with significant intraseasonal waning (VE decline from 53% to 12% by time since vaccination), but high protection (92%) again…
DOI: 10.2807/ese.18.05.20389-en -
Influenza Vaccine Effectiveness in Preventing Influenza-associated Hospitalizations During Pregnancy: A Multi-country Retrospective Test Negative Design Study, 2010–2016
A multicountry retrospective test-negative design study (PREVENT) across 2010–2016 estimated influenza vaccine effectiveness against laboratory-confirmed influenza–associated hospitalizations in pregnant women, finding an overall adjusted VE of 40% with substantial variation by …
DOI: 10.1093/cid/ciy737 -
Effectiveness of trivalent and monovalent influenza vaccines against laboratory-confirmed influenza infection in persons with medically attended influenza-like illness in Bavaria, Germany, 2010/2011 season
Trivalent seasonal influenza vaccines were about 70% effective against laboratory-confirmed influenza among medically attended ILI patients in Bavaria during 2010/2011, while monovalent vaccines from 2009/2010 showed limited protection against A(H1N1)pdm09.
DOI: 10.1017/s0950268812002282 -
Influenza vaccination during pregnancy for prevention of influenza confirmed illness in the infants: A systematic review and meta-analysis
This systematic review and meta-analysis evaluates the effectiveness of influenza vaccination during pregnancy in preventing laboratory-confirmed influenza infection and associated hospitalizations in infants under 6 months old, finding a 48% reduction in infection risk and a 72…
DOI: 10.1080/21645515.2017.1345385 -
Estimating vaccine effectiveness in preventing laboratory‐confirmed influenza in outpatient settings in South Africa, 2015
In a South African outpatient test-negative case-control study during the 2015 influenza season, trivalent influenza vaccine effectiveness was 46.2% against any laboratory-confirmed influenza and 53.5% against influenza A(H1N1)pdm09, with low overall vaccine coverage of 3.2%.
DOI: 10.1111/irv.12436 -
Effectiveness of the pandemic H1N1 influenza vaccines against laboratory-confirmed H1N1 infections: Population-based case–control study
This population-based case-control study evaluates the effectiveness of the pandemic H1N1 influenza vaccines against laboratory-confirmed H1N1 infections in Manitoba, finding an overall effectiveness of 86% when vaccination occurred at least 14 days prior to testing.
DOI: 10.1016/j.vaccine.2011.08.068 -
Live‐attenuated influenza vaccine effectiveness against hospitalization in children aged 2–6 years, the first three seasons of the childhood influenza vaccination program in England, 2013/14–2015/16
The first three seasons of England's childhood LAIV vaccination program were associated with 50.1% adjusted vaccine effectiveness against laboratory-confirmed influenza hospitalization in 2-6-year-olds, with positive estimates by age group and influenza type, though risk-stratif…
DOI: 10.1111/irv.12990 -
The effectiveness of influenza vaccination in preventing hospitalisation in children in Western Australia
This study evaluates the effectiveness of the trivalent inactivated influenza vaccine (TIV) in preventing hospitalizations due to laboratory-confirmed influenza in children in Western Australia, finding a vaccine effectiveness of 62.3% with low vaccine uptake.
DOI: 10.1016/j.vaccine.2015.10.122 -
Effectiveness of Live Attenuated vs Inactivated Influenza Vaccines in Children During the 2012-2013 Through 2015-2016 Influenza Seasons in Alberta, Canada
This study compares the effectiveness of live attenuated influenza vaccine (LAIV) and inactivated influenza vaccine (IIV) in preventing laboratory-confirmed influenza among children aged 2 to 17 years during the 2012-2013 to 2015-2016 influenza seasons in Alberta, Canada, findin…
DOI: 10.1001/jamapediatrics.2018.1514 -
Acute Respiratory Illness in Patients With COPD and the Effectiveness of Influenza Vaccination
This randomized controlled study investigates the effectiveness of influenza vaccination in preventing influenza-related acute respiratory illness (ARI) in patients with chronic obstructive pulmonary disease (COPD), demonstrating a significant reduction in influenza-related ARI …
DOI: 10.1378/chest.125.6.2011 -
Adverse effects associated with influenza vaccination in patients with COPD: a randomized controlled study
This study assesses the frequency and types of adverse reactions following influenza vaccination in patients with COPD, finding minimal local reactions and no significant impact on lung function or exercise capacity.
DOI: 10.1111/j.1440-1843.2004.00616.x -
Induction of Cross-Neutralizing Antibody Against H5N1 Virus After Vaccination with Seasonal Influenza Vaccine in COPD Patients
This study investigates the induction of cross-neutralizing antibodies against the H5N1 virus in elderly COPD patients following vaccination with a seasonal influenza vaccine, revealing that vaccination, rather than influenza illness, is responsible for the observed antibody res…
DOI: 10.1089/vim.2009.0082 -
A nasally administered trivalent inactivated influenza vaccine is well tolerated, stimulates both mucosal and systemic immunity, and potentially protects against influenza illness
A multicenter, randomized, double-blind, placebo-controlled trial in healthy adults shows that a nasally administered meningococcal outer membrane protein-adjuvanted trivalent influenza vaccine (OMP-TIV) is well tolerated, immunogenic at day 28, and may reduce culture-confirmed …
DOI: 10.1016/j.vaccine.2010.12.100 -
Effects of oral intake of plasmacytoid dendritic cells-stimulative lactic acid bacterial strain on pathogenesis of influenza-like illness and immunological response to influenza virus
Daily intake of yogurt containing Lactococcus lactis JCM5805 reduced cough and feverishness in influenza-like illness and enhanced IFN-α and ISG15 responses to influenza A/H1N1 in healthy adults.
DOI: 10.1017/s0007114515002408 -
Randomized, Double‐Blind Controlled Phase 3 Trial Comparing the Immunogenicity of High‐Dose and Standard‐Dose Influenza Vaccine in Adults 65 Years of Age and Older
A multicenter, randomized, double-blind Phase 3 trial showed that a high-dose influenza vaccine (60 µg HA per strain) elicited significantly higher humoral immunogenicity (HAI GMTs and seroconversion/seroprotection rates) than the standard-dose vaccine in adults aged 65 and olde…
DOI: 10.1086/599790 -
2009 H1N1 influenza vaccines in pregnant women: The French Pharmacovigilance survey
This study investigates adverse drug reactions (ADRs) reported in pregnant women following the administration of the 2009 H1N1 influenza vaccine in France, revealing a total of 30 serious ADRs including intra-uterine deaths and spontaneous abortions, but concluding that the rate…
DOI: 10.1016/j.vaccine.2010.12.011 -
Large scale safety study of a liquid hexavalent vaccine (D-T-acP–IPV–PRP∼T–HBs) administered at 2, 4, 6 and 12–14 months of age
This study evaluates the safety and tolerability of a new liquid hexavalent vaccine administered to 1783 children in Germany, finding it generally well tolerated with low rates of serious adverse events.
DOI: 10.1016/s0264-410x(01)00344-9 -
The Facts About Vaccine Safety
This article analyzes US Vaccine Injury Compensation Program (VICP) data to quantify the risk of serious vaccine-related adverse events per million doses and to illustrate the vaccine risk-benefit balance.
DOI: 10.1093/cid/ciaa697 -
Safety and immunogenicity of an alum-adjuvanted whole-virion H7N9 influenza vaccine: a randomized, blinded, clinical trial
An expanded phase I randomized, blinded, single-centre trial in China found that an alum-adjuvanted whole-virion H7N9 influenza vaccine is safe and strongly immunogenic across three antigen doses, with enhanced antibody responses after a second dose.
DOI: 10.1016/j.cmi.2020.07.033 -
Immunogenicity and safety of a pentavalent acellular pertussis combined vaccine including diphtheria, tetanus, inactivated poliovirus and conjugated Haemophilus Influenzae type b polysaccharide for primary vaccination at 2, 3, 4 or 3, 4, 5 months of age in infants in China☆☆☆
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.
DOI: 10.1016/j.vaccine.2010.12.103 -
A phase I clinical trial of a PER.C6® cell grown influenza H7 virus vaccine
Two-dose, cell-based PER.C6 H7N1 influenza vaccine was safe and well tolerated in healthy adults; aluminium hydroxide adjuvant increased the proportion of antibody responders but overall immunogenicity remained low and did not meet licensing criteria.
DOI: 10.1016/j.vaccine.2009.01.116 -
Maternal immunization in Argentina: A storyline from the prospective of a middle income country
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.
DOI: 10.1016/j.vaccine.2015.07.109 -
Surveillance of adverse events following immunisation in Australia annual report, 2022
A national registry-based analysis of non-COVID-19 adverse events following immunisation (AEFI) in Australia for 2022, detailing demographic patterns, reporting sources, vaccine-associated adverse events, signals (notably hypersensitivity and vaccination errors), the impact of n…
DOI: 10.33321/cdi.2025.49.043 -
Safety of Recombinant Influenza Vaccine Compared to Inactivated Influenza Vaccine in Adults: An Observational Study
An observational retrospective cohort study using Kaiser Permanente data comparing safety outcomes after recombinant influenza vaccine (RIV3) versus standard inactivated influenza vaccine (IIV3) in adults, finding no safety concerns and a lower rate of all-cause hospitalization …
DOI: 10.1093/ofid/ofaa179 -
Guillain-Barré Syndrome and Vaccination: Usually Unrelated
A narrative review of epidemiological data on Guillain-Barré syndrome (GBS) and vaccines concludes that GBS is usually triggered by antecedent infections rather than vaccination; clear causal associations were limited to the obsolete neural-tissue rabies vaccine and the 1976 swi…
DOI: 10.1177/001857870003500214