Three RCTs were included in the review (451 participants). Methods of randomisation and allocation concealment were adequately reported in one trial, partially addressed in one trial, and unclear in the third trial. All trials were double-blinded.
Two of the RCTs reported a statistically significant benefit of intranasal zinc in the resolution of symptoms at day three. One trial reported an improvement in total symptom score at day one (p=0.002).
The pooled risk ratio for any symptoms persisting at day three favoured intranasal zinc compared with placebo, but the results were not statistically significant using a random-effects analysis (risk estimate 0.62, 95% CI 0.18 to 2.19; Ι²=99%; three RCTs).
Subgroup analysis of the two high dose zinc studies for any symptoms at day three (using a fixed-effect model) showed a significant improvement in favour of zinc compared with placebo (RR 0.43, 95% CI 0.35 to 0.53).
Adverse events, including nasal stinging and burning, were more common in the treatment group in one of the trials. The two other trials did not demonstrate significant differences in adverse events between treatment groups.