Summary of findings for the main comparison. Virus vaccines compared to placebo for preventing the common cold in healthy people.

Virus vaccines compared to placebo for preventing the common cold in healthy people
Patient or population: healthy people Settings: outpatients at Great Lakes Naval Training Center Intervention: virus vaccines for preventing the common cold¹ Comparison: placebo
Outcomes	Illustrative comparative risks* (95% CI)		Relative effect (95% CI)	No. of participants (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Placebo	Virus vaccines for preventing the common cold
Incidence of the common cold Number of participants with common cold by group Follow‐up: mean 9 weeks	Study population		RR 0.95 (0.45 to 2.02)	2307 (1 study)²	⊕⊕⊝⊝ low³ ⁴
	12 per 1000	11 per 1000 (5 to 24)
Vaccine safety	The study stated that there were no adverse events related to the vaccine.			2307 (1 study)²	⊕⊕⊝⊝ low³ ⁵
Mortality related to the vaccine ‐ not reported	See comments	See comments	See comments	See comments	See comments	The included study did not report this outcome.
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; RR: risk ratio
GRADE Working Group grades of evidence. High quality: Further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: We are very uncertain about the estimate.

¹Adenovirus vaccine used for preventing the common cold.
 ²Griffin 1970.
 ³Downgraded one level due to high risk of bias for this outcome.
 ⁴Downgraded one level due to imprecision: few events (N = 27) and wide 95% confidence interval.
 ⁵Downgraded one level due to imprecision: zero events reported in a narrative fashion.