Question explored with the scientific record
Conversation so far
- 1 does the flu vaccine work
- 2 show me only rct TRIALS
- 3 so any evidence it works on hard endpoints
Answered on this page ↓
so any evidence it works on hard endpoints
The short version: the evidence for flu vaccine reducing hard endpoints like death is almost entirely observational, not from randomized trials, and the observational studies are riddled with healthy-user bias.
The one cluster-randomized trial here tests vaccinating care home staff, not residents, and found a 5% absolute reduction in resident deaths during the 2003-04 flu season but no effect in 2004-05 when flu was mild [22]. That is a real result for one season in one setting, but it does not answer whether vaccinating the elderly themselves reduces mortality.
The rest of the mortality evidence is observational. The 2009 Kaiser study that tried to correct for healthy-user bias found the vaccine reduced all-cause mortality by only 4.6% during flu season, not the 50% that uncorrected studies claim [23]. A bias-adjusted meta-analysis from 2014 found the same pattern: after correcting for selection bias, the mortality benefit shrank to a 25% reduction in all-cause mortality, with wide confidence intervals [17]. The 2001 study of three health plans reported 35-61% mortality reduction in the elderly, but those are raw observational numbers that do not control for the fact that vaccinated people are healthier [4].
| Outcome | Study type | Best estimate | Source |
|---|---|---|---|
| All-cause mortality, elderly | Observational, bias-corrected | ~25% reduction | [17] |
| All-cause mortality, elderly | Observational, uncorrected | 35-61% reduction | [4] |
| All-cause mortality, elderly | Observational, bias-corrected | 4.6% reduction | [23] |
| Resident death, nursing home | Cluster RCT (staff vaccinated) | 5% absolute reduction (1 season only) | [22] |
My call: no randomized trial has ever tested whether flu vaccination prevents death in healthy adults or children. The observational evidence is contradictory and shrinks dramatically when bias is accounted for. Confidence: low that the vaccine reduces all-cause mortality in the general population.
Sources examined 32
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Influenza vaccine effectiveness against influenza-associated hospitalization in 2015/16 season, Beijing, China
This study estimates the effectiveness of the influenza vaccine against hospitalization due to influenza in Beijing during the 2015/16 season, finding that vaccination did not provide effective protection.
DOI: 10.1016/j.vaccine.2017.03.084 -
Interim estimates of the effectiveness of influenza vaccination against influenza‐associated hospitalization in children in Hong Kong, 2015–16
In an interim test-negative study of 2,049 hospitalized children in Hong Kong in 2015-16, influenza vaccination was associated with 79.0% estimated effectiveness against influenza-associated hospitalization.
DOI: 10.1111/irv.12399 -
Effects of previous influenza vaccination on subsequent readmission and mortality in elderly patients hospitalized with pneumonia
An observational, retrospective cohort study of 12,566 elderly Medicare beneficiaries hospitalized with pneumonia, finding that influenza vaccination before hospitalization is associated with lower subsequent mortality and hospital readmission compared with unknown vaccination s…
DOI: 10.1016/s0002-9343(03)00440-6 -
Influenza Vaccine Effectiveness in Preventing Hospitalizations and Deaths in Persons 65 Years or Older in Minnesota, New York, and Oregon: Data from 3 Health Plans
This study assesses the effectiveness of influenza vaccination in reducing hospitalizations and deaths among elderly individuals aged 65 and older across three health plans in Minnesota, New York, and Oregon, finding significant reductions in both outcomes during two influenza s…
DOI: 10.1086/323085 -
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 -
An overview of new data on the relative effectiveness of flu vaccines in vulnerable populations
Adjuvanted influenza vaccine in elderly nursing-home residents reduced all-cause hospitalizations by 6% and pneumonia-or-influenza hospitalizations by 21% compared with standard-dose vaccine, with no difference in respiratory-related hospitalizations.
DOI: 10.70270/5tq0xqx -
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 -
Influenza vaccination rates for hospitalised patients: a multiyear quality improvement effort
This study aimed to improve influenza vaccination rates among hospitalized patients at the White River Junction VA Medical Center through a multiyear quality improvement initiative that successfully increased vaccination rates from approximately 60% to 90% over six influenza sea…
DOI: 10.1136/bmjqs-2014-003556 -
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 -
Interventions to prevent pneumonia in older adults
Interventions to prevent pneumonia in older adults—including capsaicin, amantadine, ACE inhibitors, cilostazol, folic acid, oral hygiene, and vaccines—are reported to reduce pneumonia incidence or hospitalization in older adults, particularly those with silent aspiration or immo…
DOI: 10.1111/j.1447-0594.2004.00162.x -
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.
DOI: 10.1093/ofid/ofy229.2194 -
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 -
Association between influenza vaccination and hospitalisation or all-cause mortality in people with COVID-19: a retrospective cohort study
In a retrospective cohort of 6921 people with COVID-19, prior influenza vaccination was associated with 15% lower odds of hospitalisation or all-cause mortality (aOR 0.85) and 24% lower odds of all-cause mortality (aOR 0.76).
DOI: 10.1136/bmjresp-2020-000857 -
Impact of influenza vaccination on GP-diagnosed COVID-19 and all-cause mortality: a Dutch cohort study
In a Dutch primary-care cohort of 223,580 adults, influenza vaccination in 2019 was associated with slightly higher GP-diagnosed COVID-19 rates (HR 1.15; 95% CI 1.08 to 1.22) but slightly lower all-cause mortality (HR 0.90; 95% CI 0.83 to 0.97).
DOI: 10.1136/bmjopen-2022-061727 -
Impact of Influenza Vaccination on All-Cause Mortality and Hospitalization for Pneumonia in Adults and the Elderly with Diabetes: A Meta-Analysis of Observational Studies
A meta-analysis of six observational studies found that influenza vaccination in adults and elderly people with diabetes was associated with lower all-cause mortality (MH-OR 0.54, 95% CI 0.40-0.74) and lower hospitalization for pneumonia (MH-OR 0.89, 95% CI 0.80-0.98).
DOI: 10.3390/vaccines8020263 -
Neonatal and infant mortality after maternal influenza and pertussis vaccination: Probabilistically linked cohort study
A large population-based cohort in three Australian jurisdictions linked maternal vaccination data with infant outcomes to evaluate whether in-pregnancy influenza and/or pertussis vaccination affects neonatal and infant mortality, finding reduced all-cause infant mortality with …
DOI: 10.1080/21645515.2025.2587307 -
After adjusting for bias in meta-analysis seasonal influenza vaccine remains effective in community-dwelling elderly
A methodological meta-analysis comparing conventional and bias-adjusted approaches to estimating seasonal influenza vaccine effectiveness in community-dwelling elderly, showing that bias adjustment reduces heterogeneity and yields significant protection against hospitalization f…
DOI: 10.1016/j.jclinepi.2014.02.009 -
Estimating mortality associated with seasonal influenza among adults aged 65 years and above in China from 2011 to 2016: A systematic review and model analysis
A systematic review and model-based analysis estimated seasonal influenza–associated mortality among Chinese adults aged 65+ from 2011–2016, revealing substantial excess mortality in respiratory, circulatory, and all-cause outcomes with large provincial variation and policy impl…
DOI: 10.1111/irv.13067 -
O-050: Incidence of benzodiazepine and related drug use in persons with and without Alzheimer's disease: the MEDALZ study
This study systematically reviews the efficacy, safety, and tolerability of commonly prescribed urological drugs for treating lower urinary tract symptoms (LUTS) in elderly patients, finding significant associations between certain vaccinations and reduced all-cause mortality in…
DOI: 10.1016/s1878-7649(15)30063-2 -
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…
DOI: 10.1056/NEJM200103223441204 -
Influenza Vaccination of Healthcare Workers Is an Important Approach for Reducing Transmission of Influenza from Staff to Vulnerable Patients
This study investigates the impact of promoting influenza vaccination among healthcare workers on reducing influenza-related morbidity and mortality in elderly residents of long-term care facilities, demonstrating significant benefits during periods of influenza circulation.
DOI: 10.1371/journal.pone.0169023 -
Effectiveness of an influenza vaccine programme for care home staff to prevent death, morbidity, and health service use among residents: cluster randomised controlled trial
A cluster-randomised trial in UK care homes found that vaccinating care home staff against influenza reduced resident mortality, influenza-like illness, GP consultations for influenza-like illness, and hospital admissions during periods of influenza activity in the 2003-04 seaso…
DOI: 10.1136/bmj.39010.581354.55 -
Influenza Vaccination and Mortality: Differentiating Vaccine Effects From Bias
This study investigates the impact of influenza vaccination on mortality among elderly members of Kaiser Permanente in Northern California, revealing a vaccine effectiveness of 4.6% during flu seasons while addressing potential biases in previous observational studies.
DOI: 10.1093/aje/kwp173 -
Influenza-associated disease burden in mainland China: a systematic review and meta-analysis
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…
DOI: 10.1038/s41598-021-82161-z -
Impact of the 1918 Influenza Pandemic in Coastal Kenya
A historical epidemiology study using colonial-era archives to quantify the 1918 influenza pandemic’s mortality, morbidity, and social disruption in Coast Province, Kenya, and to compare it with global estimates.
DOI: 10.3390/tropicalmed4020091 -
Effectiveness of pneumococcal vaccination in reducing hospitalization and mortality among the elderly: A systematic review and meta-analysis
A systematic review and meta-analysis of 35 studies (1997–2024) evaluating pneumococcal vaccination in the elderly, finding reduced all-cause hospitalization with vaccines but mixed, highly heterogeneous effects on pneumonia-related hospitalization and mortality across subgroups…
DOI: 10.1080/21645515.2025.2561315 -
Epidemiological and Virological Characteristics of Influenza in Chongqing, China, 2011-2015
This study investigates the epidemiological and virological characteristics of influenza in Chongqing, China, from 2011 to 2015, revealing significant infection rates particularly among school-aged children and highlighting the need for targeted vaccination strategies.
DOI: 10.1371/journal.pone.0167866 -
Multisite virological influenza surveillance in India: 2004–2008
This study presents a comprehensive multisite surveillance of influenza in India from 2004 to 2008, revealing significant seasonal patterns, subtype distribution, and genetic characteristics of circulating strains, which have implications for vaccination strategies.
DOI: 10.1111/j.1750-2659.2011.00293.x -
Antibody responses and HIV-1 viral load in HIV-1-seropositive subjects immunised with either the MF59-adjuvanted influenza vaccine or a conventional non-adjuvanted subunit vaccine during highly active antiretroviral therapy
This study investigates the immunological and virological effects of the MF59-adjuvanted influenza vaccine compared to a conventional non-adjuvanted vaccine in HIV-1-seropositive individuals undergoing highly active antiretroviral therapy, finding that the adjuvanted vaccine ind…
DOI: 10.1016/s0264-410x(03)00408-0 -
HIV virological suppression influences response to the AS 03‐adjuvanted monovalent pandemic influenza A H 1 N 1 vaccine in HIV ‐infected children
This study investigates the safety and immunogenicity of the AS03-adjuvanted pandemic H1N1 vaccine in HIV-infected children, finding that HIV virological suppression significantly enhances seroconversion rates and immunological response.
DOI: 10.1111/irv.12243 -
Mexico's experience when vaccinating against Avian Influenza: Advantages, disadvantages, and needs. Proceeding of The First International Avian Influenza Summit, University of Arkansas- October 16-17, 2023”
Vaccination against avian influenza in Mexico provides systemic protection and mortality reduction but may permit endemic transmission, highlighting the need for vaccines that induce mucosal IgA, better strain matching, and improved diffusion of virology information.
DOI: 10.51585/gtop.2023.1.0032 -
Changing Perceptions: of Pandemic Influenza and Public Health Responses
A historical/public health analysis tracing how understandings of influenza and related public policy have evolved over 500 years—from meteorological and contagion theories to virology and securitized governance—highlighting shifts in policy, funding, and global health governanc…
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