Question explored with the scientific record
Is an annual flu shot necessary
The annual flu shot is not "necessary" for everyone; it is a risk-benefit decision that depends heavily on your age and health, with the evidence showing real but modest and highly variable protection.
The strongest evidence for benefit is in the elderly and high-risk groups. A meta-analysis of observational studies in diabetics found vaccination associated with roughly half the all-cause mortality (odds ratio 0.54) [1]. A Scottish ecological study linked the policy of vaccinating everyone over 65 to significant reductions in excess deaths and COPD hospitalizations [4]. A 2004 UK cohort of people over 75 found vaccination blunted the rise in deaths during flu season [2]. A 2025 Australian cohort even linked maternal vaccination to lower infant mortality [3].
But the protection is not uniform. In Israel, the trivalent vaccine showed no significant effectiveness in 2014/15 and 2015/16 overall, and no protection in children [8]. In the US 2018-19 season, effectiveness was just 29% overall, and only 11% against the dominant H3N2 strain [9]. Protection also wanes significantly within a season, dropping to near zero for H3N2 by about five months [11]. One South African study concluded its apparent benefit in the elderly could be explained by "healthy-user bias" [5].
| Group | Vaccine effectiveness (typical range) |
|---|---|
| Healthy adults, well-matched season | 40-60% [6][7][10] |
| Elderly, against H3N2 | Often not significant [12] |
| Children | Often not significant [8] |
| Hospitalization prevention, adults | 50-71% [13][14] |
The evidence is almost entirely observational, funded or influenced by manufacturers, and rarely compares vaccinated against truly unvaccinated people over the long term. The burden of proof for annual universal vaccination is not met.
My call: For the elderly and high-risk, the shot likely reduces serious outcomes and is a reasonable choice. For healthy children and working-age adults, the benefit is modest, unreliable, and not "necessary." Confidence: moderate.
Sources used 14
-
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 -
Effect of influenza vaccination on excess deaths occurring during periods of high circulation of influenza: cohort study in elderly people
Among 24,535 people aged over 75 in UK primary care, influenza vaccination blunted the rise in all-cause mortality during high influenza circulation; the estimated effectiveness against influenza-associated death was 83%, though imprecise.
DOI: 10.1136/bmj.38198.594109.ae -
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 -
Modelling the population effectiveness of the national seasonal influenza vaccination programme in Scotland: The impact of targeting all individuals aged 65 years and over
Using Scottish routine data from 1981-2012, Poisson GAM models estimate that the mid-2000 policy extending influenza vaccination to all people aged 65+ was associated with significant reductions in excess all-cause mortality, cardiovascular and COPD mortality, and COPD hospitali…
DOI: 10.1111/irv.12583 -
Effectiveness of influenza vaccination in the elderly in South Africa
In a nested case-control study of medically insured elderly in South Africa, influenza vaccination was associated with fewer serious complications after full adjustment, but sensitivity analysis suggested healthy-user bias could explain the findings, so the data were inconclusiv…
DOI: 10.1017/s0950268808001386 -
Influenza Vaccine Effectiveness in the United States During 2012-2013: Variable Protection by Age and Virus Type
This study evaluates the effectiveness of the influenza vaccine during the 2012-2013 season in the United States, revealing variable protection across different age groups and virus types.
DOI: 10.1093/infdis/jiu647 -
Estimating the Influenza Vaccine Effectiveness against Medically Attended Influenza in Clinical Settings: A Hospital-Based Case-Control Study with a Rapid Diagnostic Test in Japan
This study estimates the effectiveness of the influenza vaccine against medically attended influenza in Japan using a test-negative case-control design with rapid diagnostic tests, finding an overall vaccine effectiveness of 47.6% during the 2010/11 influenza season.
DOI: 10.1371/journal.pone.0052103 -
Effectiveness of influenza vaccine in preventing medically-attended influenza virus infection in primary care, Israel, influenza seasons 2014/15 and 2015/16
Trivalent inactivated influenza vaccine showed no significant overall effectiveness in Israel in 2014/15 or 2015/16, but in 2015/16 it was moderately effective against A(H1N1)pdm09 in adults, with no significant protection in children.
DOI: 10.2807/1560-7917.es.2018.23.7.17-00026 -
Update From the Advisory Committee on Immunization Practices
ACIP's June 2019 meeting update reports vaccine policy votes on HPV, pneumococcal, influenza, hepatitis A, and meningococcal vaccines, plus measles, zoster, and dengue vaccine surveillance and trial evidence.
DOI: 10.1093/jpids/piz058 -
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 -
Intraseason Waning of Influenza Vaccine Protection: Evidence From the US Influenza Vaccine Effectiveness Network, 2011–2012 Through 2014–2015
Influenza vaccine effectiveness wanes with increasing time since vaccination across influenza A(H3N2), A(H1N1)pdm09, and B viruses, as observed in the US Influenza VE Network from 2011-12 through 2014-15.
DOI: 10.1093/cid/ciw816 -
Influenza vaccine effectiveness in older adults compared with younger adults over five seasons
This study conducted a pooled analysis of influenza vaccine effectiveness over five seasons, comparing older adults (aged 65 years and above) with younger adults (aged 18-49 years), and found no significant differences in vaccine effectiveness between the two groups across vario…
DOI: 10.1016/j.vaccine.2018.01.045 -
997. Protection of Unvaccinated Individuals by Influenza Vaccine Coverage of Household Contacts
In a 2015-2016 test-negative study, influenza vaccination reduced hospitalization for PCR-confirmed influenza among adults by 50%, with high effectiveness in neurologic, metabolic, and cardiovascular conditions but lower, non-significant effectiveness in immunosuppressed/maligna…
DOI: 10.1093/ofid/ofy210.834 -
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