Question explored with the scientific record
Should a 100 year old take flu vax
A 100-year-old is at real risk from flu, and the evidence that the shot prevents death at that age is thin and conflicted.
The danger is not hypothetical. In US surveillance, adults 85 and older were hospitalized with lab-confirmed flu at 2.2 to 6.4 times the rate of 65-to-74-year-olds, and had about double the adjusted odds of dying in hospital or being sent to hospice [7]. Chinese modeling found flu-linked all-cause mortality of about 123 per 100,000 in the 65-plus group versus about 3 per 100,000 under 65 [1]. Flu also triggers heart attacks: a sixfold rise in the week after infection, highest in people over 65 [3].
The protection evidence is weaker than the marketing. A bias-adjusted meta-analysis of 14 cohort studies in community-dwelling elderly found the shot cut flu/pneumonia hospitalizations and all-cause deaths, but the effect on lab-confirmed flu and flu-like illness did not survive adjustment [2]. A Korean case-control study found no significant effectiveness at all in adults 65 and older [4]. A 2019 systematic review of 22 studies called the overall evidence low quality, with too much heterogeneity to pool hospital or heart outcomes [6]. One review even flagged higher mortality in those vaccinated in the current season [5]. No retrieved study isolates the 100-plus group, and none is a randomized trial with death as the endpoint.
| Group | Flu hospitalization rate | vs age 65-74 |
|---|---|---|
| 65-74 | 101-417 per 100,000 | reference |
| 75-84 | 209-1,264 per 100,000 | 1.4-3.0x |
| 85+ | 562-2,651 per 100,000 | 2.2-6.4x |
My call: for a 100-year-old, the risk of flu is high and the shot's benefit is plausible but unproven at that age, so it is a reasonable personal choice, not a mandate, and the decision belongs to the patient and family. Confidence: low.
Sources used 7
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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 -
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 -
Acute Myocardial Infarction after Laboratory-Confirmed Influenza Infection
In Ontario adults aged 35 and older, using a self-controlled case-series with laboratory-confirmed influenza testing, the study found a strong, time-limited increase in hospitalization for acute myocardial infarction within 7 days after influenza detection, especially in days 1–…
DOI: 10.1056/nejmoa1702090 -
Case-Control Study of the Effectiveness of the 2010-2011 Seasonal Influenza Vaccine for Prevention of Laboratory-Confirmed Influenza Virus Infection in the Korean Adult Population
A retrospective matched case-control study in 1,449 South Korean adults found the 2010-2011 seasonal influenza vaccine was 45.8-49.5% effective against laboratory-confirmed influenza, especially influenza A, with no significant effect in adults ≥65 years or against influenza B.
DOI: 10.1128/cvi.00009-13 -
Healthy-vaccinated effect
The study by Casado et al. demonstrates that repeated influenza vaccination significantly reduces the risk of severe influenza in older hospitalized patients, although it raises concerns about increased mortality in those vaccinated in the current season.
DOI: 10.1503/cmaj.69406 -
Impact of influenza vaccination on healthcare utilization – A systematic review
A systematic review evaluating the impact of seasonal influenza vaccination on healthcare utilization in older adults (65+), finding modest protection for outpatient visits but substantial heterogeneity and overall low-quality evidence that prevents a definitive conclusion about…
DOI: 10.1016/j.vaccine.2019.04.051 -
Age-Related Differences in Hospitalization Rates, Clinical Presentation, and Outcomes Among Older Adults Hospitalized With Influenza—U.S. Influenza Hospitalization Surveillance Network (FluSurv-NET)
Among adults aged ≥65 years hospitalized with laboratory-confirmed influenza, hospitalization rates and adjusted odds of pneumonia and death or transfer to hospice increased with age, with the highest rates and severity in patients aged ≥85 years.
DOI: 10.1093/ofid/ofz225