IL4 and influenza: In the systematic review and meta-analysis of studies addressing host genetic factors implicated in five common respiratory tract infectious diseases—i.e tuberculosis, influenza, respiratory syncytial virus (RSV) and SARS-CoV—published in 2015 [14], Patarčić and co-workers reported IL4 as the single result that was significant in pooled analyses, and marginally significant in disease-specific meta-analyses.