According to a study published in the Cochrane Database of Systematic Reviews, use of saline seems to be an effective method for reducing the severity of some symptoms associated with acute upper respiratory tract infections.

In this study, 5 randomized controlled trials were identified that randomised 544 children (3 studies) and 205 adults (exclusively from 2 studies). All studies compared use of saline to routine care or other nose sprays, rather than placebo. Of these, 1 large trial conducted on children showed a remarkable reduction in nasal secretion score [mean difference (MD) -0.31, 95% confidence interval (CI) -0.48 to -0.14)] and nasal breathing (obstruction) score (MD -0.33, 95% CI -0.47 to -0.19) in the saline group.Source: King D, Mitchell B, Williams CP, et al. Saline nasal irrigation for acute upper respiratory tract infections. Cochrane Database Syst Rev. 2015 Apr 20;(4):CD006821.