Influenza (Flu) Vaccines — Study Scorecard

Cochrane Review: Flu Vaccines in Adults

Jefferson et al., Cochrane Database 2018

8/9

Sample size N = 70,000+ (52 trials)

Follow-up 6 months

Reported efficacy 59% against confirmed influenza; ARR ~1.2%; NNV: 71

Funding Independent (Cochrane Collaboration)

8/9 criteria met (89%)

Criterion	Met
Control Group	✅
Randomized	✅
Double-Blind	✅
Placebo-Controlled	✅
Large Sample (1,000+)	✅
Long Follow-up (1yr+)	❌
Independent Funding	✅
Peer-Reviewed	✅
Results Reproduced	✅

Flu vaccine reduces cases from ~2.3% to ~1.1% in the vaccinated group.

High-Dose vs. Standard Flu Vaccine (65+)

DiazGranados et al., NEJM 2014

6/9

Sample size N = 31,989

Follow-up 7 months

Reported efficacy 24.2% more effective than standard-dose in adults 65+

Funding Sanofi Pasteur (manufacturer)

6/9 criteria met (67%)

Criterion	Met
Control Group	✅
Randomized	✅
Double-Blind	✅
Placebo-Controlled	❌
Large Sample (1,000+)	✅
Long Follow-up (1yr+)	❌
Independent Funding	❌
Peer-Reviewed	✅
Results Reproduced	✅

Head-to-head comparison, not placebo-controlled.

Flu Vaccine Efficacy: Systematic Review

Osterholm et al., Lancet Infect Dis 2012

8/9

Sample size N = 50,000+

Follow-up 6 months

Reported efficacy 59% against confirmed influenza in adults 18–65

Funding Independent

8/9 criteria met (89%)

Criterion	Met
Control Group	✅
Randomized	✅
Double-Blind	✅
Placebo-Controlled	✅
Large Sample (1,000+)	✅
Long Follow-up (1yr+)	❌
Independent Funding	✅
Peer-Reviewed	✅
Results Reproduced	✅

CDC FluView Annual Effectiveness Studies

CDC Influenza Division, MMWR (2004–present)

6/9

Sample size N = 10,000+ per season

Follow-up 8 months per season

Reported efficacy 10–60% depending on season strain match

Funding Independent (CDC / federal)

6/9 criteria met (67%)

Criterion	Met
Control Group	✅
Randomized	❌
Double-Blind	❌
Placebo-Controlled	❌
Large Sample (1,000+)	✅
Long Follow-up (1yr+)	✅
Independent Funding	✅
Peer-Reviewed	✅
Results Reproduced	✅

Observational design; efficacy varies significantly season-to-season based on strain match.

Side-by-Side Comparison

Criterion	Cochrane Review: Flu Vaccines in Adults	High-Dose vs. Standard Flu Vaccine (65+)	Flu Vaccine Efficacy: Systematic Review	CDC FluView Annual Effectiveness Studies
Control Group	✅	✅	✅	✅
Randomized	✅	✅	✅	❌
Double-Blind	✅	✅	✅	❌
Placebo-Controlled	✅	❌	✅	❌
Large Sample (1,000+)	✅	✅	✅	✅
Long Follow-up (1yr+)	❌	❌	❌	✅
Independent Funding	✅	❌	✅	✅
Peer-Reviewed	✅	✅	✅	✅
Results Reproduced	✅	✅	✅	✅
Total score	8/9	6/9	8/9	6/9

Methodology note: A lower score does not mean a vaccine is unsafe or ineffective. It means the published evidence has methodological gaps — shorter follow-up, manufacturer funding, or non-standard controls. We evaluate methodology only. Consult your healthcare provider about vaccination decisions.

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