Meta-analysisindependent cross-checkabstract only checked I-INTB-13 standard review
Flu vaccines in healthy adults
Vaccines for preventing influenza in healthy adults.
Overview
Demicheli V et al.. Cochrane Database Syst Rev 2018 · PMID 29388196 · DOI 10.1002/14651858.CD001269.pub6
Vaccination roughly halves confirmed influenza (2.3% to 0.9%); absolute benefit is modest.
Does the study support the specific claim? No · Methodological quality: high
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Assess influenza vaccines
- How was the study done?
Cochrane review
- How many people, animals or samples were studied?
52 trials, >80,000 adults
- What was actually found?
Fewer influenza cases; small effect on hospitalisation
- How large was the observed effect?
RR 0.41
- What do the results mean in everyday life?
Flu shots reduce flu but do not abolish it; nothing removes seasonal flu from a country in three weeks.
- What are the study's limitations?
Old trials; abstract only
- What does it say about Elawady's specific claim?
Contradicts both the 3-week claim and blanket vaccine rejection, while showing modest absolute benefit.
- Do the results apply to Germany and Europe?
High
- What can explicitly not be concluded from this study?
Does not address older or high-risk adults.
Scientific in-depth review
1. Full reference
- Authors
- Demicheli V et al.
- Journal
- Cochrane Database Syst Rev
- Year
- 2018
- Identifier
- PMID 29388196 DOI 10.1002/14651858.CD001269.pub6
- Verification
- verified – PubMed efetch 2026-10-25
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
Declared interests in record (e.g., NIHR grant to one author); 15 included RCTs industry funded (29%)
2. Research question
What are the efficacy, effectiveness and harms of influenza vaccines in healthy adults?
3. Study design and population
- Study design
- Meta-analysis – Cochrane systematic review and meta-analysis of RCTs
- Population
Healthy adults 16-65 years incl. pregnant women
- Country
North America, South America, Europe
- Period
trials 1969-2009
- Sample size
52 trials, >80,000 people
- Inclusion and exclusion criteria
RCTs/quasi-RCTs vs placebo or no intervention
4. Methods and endpoints
- Exposure / intervention
Inactivated parenteral influenza vaccine
- Comparator
Placebo or no vaccination
- Endpoints
Influenza, influenza-like illness, hospitalisation, adverse effects
- Statistical methods
RR, GRADE
5. Actual results
- Results
Inactivated vaccines probably reduce influenza from 2.3% to 0.9% (RR 0.41, 95% CI 0.36-0.47; moderate certainty; NNV 71) and ILI from 21.5% to 18.1% (RR 0.84, 0.75-0.95; NNV 29). Small, uncertain effect on hospitalisation (RR 0.96, 0.85-1.08). Fever increased from 1.5% to 2.3%. No evidence of association with serious adverse events.
- Absolute risks
Influenza 2.3% -> 0.9%
- Authors' conclusion
Vaccinated healthy adults probably experience less influenza (from just over 2% to just under 1%); benefits for hospitalisation and work days are small and uncertain.
6. Strengths
- Cochrane methods
- Large RCT base
- GRADE
7. Weaknesses
- Old trials
- Seasonal variability
- Abstract only read
8. Risk of bias
- Orienting tool
- AMSTAR 2
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- low
- Rationale
High-quality review.
9. Assessment of the statistical interpretation
Moderate relative benefit, small absolute benefit in healthy adults; even the best available preventive measure does not eliminate seasonal influenza.
10. Relevance to the specific claim
Shows seasonal influenza cannot be abolished within weeks even with vaccines; contradicts the 'three weeks' claim. Also shows vaccines reduce influenza (relevant to C-SRC-56).
11. Independent contrary findings
Absolute benefit in healthy adults is modest - a fair point for vaccine sceptics.
12. Transferability to Germany and Europe
High.
13. Overall methodological judgement
Best summary of influenza vaccine effects in healthy adults.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | high |
| Risk of bias | low |
| Precision of results | high |
| Directness | direct |
| Reproducibility | replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Effects in older and high-risk groups (not in this review).
15. Linked fact checks
- He could stop kidney failure and dialysis in all of Egypt within two months and prevent seasonal influenza within three weeks. – Studies contradicting or limiting the claim
- There are to be no vaccinations: vaccinations, medicines and herbs are forbidden. – Studies contradicting or limiting the claim