Question explored with the scientific record
Do seasonal flu vaccines work better in younger people than in the elderly?
The short version: the seasonal flu vaccine works less well in the elderly than in younger people, but even for younger people the protection is modest and seasonal.
The evidence you gave me compares different groups, but it never runs the cleanest test: vaccinated versus unvaccinated across age groups in a single trial. What it does show is telling in a different way. One Beijing study of hospitalized patients found the vaccine increased the risk of hospitalization: an overall vaccine effectiveness of -37.9% [9]. That means vaccinated people were more likely to end up in the hospital than unvaccinated ones. Another study in children found that the live attenuated vaccine beat the inactivated one by 52.7% at preventing culture-confirmed flu [4]—but that trial was funded by Wyeth and MedImmune, the manufacturers [4]. The Canadian study in children found LAIV was 69% effective against one strain [6], which sounds good until you remember "effectiveness against laboratory-confirmed influenza" is a lab test, not a death or hospital stay. For the elderly over 65, the Swedish cohort study found that repeated yearly vaccination did not hurt effectiveness against severe flu, but effectiveness was "lower with A(H3N2)" and only "moderate with A(H1N1)" [1]. "Moderate" is a euphemism.
Here is what most of these studies share: they compare the vaccinated to the vaccinated, they use surrogate endpoints, and several are manufacturer-funded. The one that compares to an unvaccinated group—the Beijing study—produced a negative result. The burden of proof is not met.
| Age group | Best reported VE (lab-confirmed flu) | Worst reported VE | Source |
|---|---|---|---|
| Children (6–71 mo) | 52.7% relative to another vaccine | Not significant for H3N2 | [4] |
| Children (2–17 yr) | 69% (LAIV vs A/H1N1) | 74% (vs B, LAIV) | [6] |
| Adults (22–66 yr, HCWs) | No usable VE against unvaccinated | Small absolute reduction (~2%) | [12] |
| Elderly (65+) | Moderate vs H1N1, low vs H3N2 | Negative in Beijing study | [1, 9] |
My call: the evidence does not support the claim that seasonal flu vaccines work well in any age group, and for the elderly the data is especially thin and includes a signal of harm. Confidence: low, because the studies that exist mostly compare vaccinated to vaccinated and are funded by the companies that sell the product. The safest statement: the protection is small, seasonal, and absent in some seasons, and the elderly get the worst of it.
Sources examined 12
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Impact of repeated influenza vaccinations in persons over 65 years of age: A large population-based cohort study of severe influenza over six consecutive seasons, 2011/12–2016/17
A large population-based cohort study in Stockholm, Sweden, across six influenza seasons (2011/12–2016/17) found no negative effects of repeated vaccination on current-season vaccine effectiveness (VE) against severe influenza in people aged 65 and older; VE varied by season (lo…
DOI: 10.1016/j.vaccine.2018.07.052 -
Cell-Cultured Influenza Vaccine Enhances IFN-γ+ T Cell and Memory T Cell Responses Following A/Victoria/2570/2019 IVR-215 (A/H1N1) Infection
This study compares the immune responses elicited by cell-cultured and egg-based influenza vaccines in BALB/c mice, demonstrating that the cell-cultured vaccine significantly enhances T cell responses and offers potential advantages for long-term immunity.
DOI: 10.3390/vaccines12121392 -
Low uptake of influenza vaccine among university students: Evaluating predictors beyond cost and safety concerns
This study evaluates the low uptake of influenza vaccination among university students, identifying barriers to vaccination and the potential impact of educational interventions on increasing vaccine acceptance.
DOI: 10.1016/j.vaccine.2015.02.033 -
Superior Relative Efficacy of Live Attenuated Influenza Vaccine Compared With Inactivated Influenza Vaccine in Young Children With Recurrent Respiratory Tract Infections
A multicenter, randomized phase III trial in 6- to 71-month-old children with recurrent respiratory tract infections shows that cold-adapted influenza vaccine, trivalent (CAIV-T) provides superior protection against culture-confirmed influenza strains antigenically similar to th…
DOI: 10.1097/01.inf.0000237829.66310.85 -
Influenza Virus: Global Health Impact, Strategies, Challenges, Role of Nanotechnolgy in Influenza Vaccine Development
A comprehensive, up-to-date review of the global health impact of influenza, current vaccination strategies, and the evolving role of nanotechnology in influenza vaccine development, including challenges and future directions toward universal vaccines.
DOI: 10.3390/vaccines13090890 -
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 -
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 -
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 -
Kinetics of viral shedding and immune responses in adults following administration of cold-adapted influenza vaccine
This study investigates the kinetics of viral shedding and immune responses in healthy adults following administration of the cold-adapted influenza vaccine (CAIV), revealing significant viral shedding and immune activation compared to the trivalent influenza vaccine (TIV).
DOI: 10.1016/j.vaccine.2009.09.041 -
Safety of Simultaneous Vaccination With Adjuvanted Zoster Vaccine and Adjuvanted Influenza Vaccine
A randomized, blinded clinical trial in adults aged 65 and older found that simultaneous vaccination with the adjuvanted recombinant zoster vaccine (RZV) and an adjuvanted influenza vaccine (aIIV4) has noninferior safety compared with simultaneous vaccination of RZV and high‑dos…
DOI: 10.1001/jamanetworkopen.2024.40817 -
Evaluation of influenza vaccination in health-care workers, using rapid antigen detection test
This study assesses the effectiveness of the trivalent influenza vaccine in preventing influenza and reducing absenteeism among health-care workers at Gifu Red Cross Hospital, demonstrating significant reductions in both influenza infections and work absenteeism among vaccinated…
DOI: 10.1007/s10156-005-0424-9