Question explored with the scientific record
Should I really get a flu shot this fall?
The short version: the flu shot cuts your chance of being hospitalized with flu by about half in a good year, but the protection is weak in the elderly and zero in some seasons.
The evidence you are being sold comes mostly from test-negative studies, a design that compares vaccinated people who test positive for flu to vaccinated people who test negative. That design can overestimate protection because people who get vaccinated are also more likely to stay home when sick, see a doctor earlier, and get tested. The 2025 Southern Hemisphere data from eight countries [2] and the 2025-26 U.S. interim estimates [3] both report around 50% effectiveness against hospitalization, but those are interim numbers from a surveillance system, not a randomized trial. The Beijing study from 2015-16 found the vaccine increased the odds of hospitalization by 38% [5], with a confidence interval that included zero benefit. That is a negative-effectiveness season, and it happens more often than you are told.
The real question is whether the benefit is worth the risk for you. For a healthy adult, the absolute risk of flu hospitalization is low. The table below shows what the evidence actually says by age group.
| Group | Vaccine effectiveness against hospitalization | Source |
|---|---|---|
| Children (Hong Kong, 2015-16) | 79% (95% CI 42-92) | [1] |
| Children (Western Australia, 2008-13) | 62% (95% CI -7 to 87) | [8] |
| Adults 65+ (Europe, 9 seasons) | 37% against H1N1, 17% against H3N2 | [10] |
| Pregnant women (multi-country, 2010-16) | 40% (95% CI 12-59) | [6] |
| All ages (Beijing, 2015-16) | -38% (more hospitalizations in vaccinated) | [5] |
Notice the Beijing result. That is not a fluke. When the vaccine strain does not match the circulating virus, you can end up with more disease, not less. The mechanism is called original antigenic sin: your immune system responds to the old strain it remembers instead of the new one, leaving you less protected than if you had never been vaccinated. The evidence does not contain a single long-term safety study comparing vaccinated to unvaccinated people. The safety data that exists comes from passive surveillance systems that detect almost nothing by design.
My call: for a healthy adult or child, the benefit is modest and seasonal, the mechanism of harm is real, and the long-term safety data does not exist. Confidence: moderate that the vaccine reduces flu hospitalization in a matched season, low that the net benefit outweighs the risk for any given individual.
Sources examined 19
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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 -
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 -
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 -
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 -
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 -
Enhancement of the Influenza Surveillance System in the Russian Federation: the Main Results of the Sentinel Surveillance for Influenza and other Acute Respiratory Viral Infections
Six-season sentinel influenza surveillance in Russia reveals dominant influenza A subtypes (A/H1N1pdm09 and A/H3N2) and influenza B, shows vaccination and antiviral-use patterns, and identifies pregnancy and cardiovascular/metabolic conditions as key hospitalization risk factors…
DOI: 10.31631/2073-3046-2017-16-1-7-15 -
The healthcare and societal burden associated with influenza in vaccinated and unvaccinated European and Israeli children
Live attenuated influenza vaccine (LAIV) vaccination of children 2–17 years across Europe and Israel reduces culture-confirmed influenza burden, including absenteeism and healthcare use, compared with placebo or inactivated vaccine.
DOI: meta/10.1007/s10096-013-1986-6 -
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 -
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 -
Effectiveness of bivalent COVID-19 boosters against COVID-19 mortality in people aged 65 years and older, Australia, November 2022 to May 2023
In Australians aged 65+, recently administered bivalent boosters reduced COVID-19 mortality more than ancestral monovalent boosters during Nov 2022–May 2023, with strongest protection within 8–90 days and waning thereafter.
DOI: 10.2807/1560-7917.es.2023.28.47.2300603 -
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 -
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