IGHG3 and infection: Different pathogens may induce variable IgG subclassresponses.[15] Viral infections induce an antibody responsepredominantly consisting of IgG1 and IgG3 while bacterialinfections are associated with the induction of IgG2 and IgG4subclasses.[16] An apparent deficiency of IgG2 has been reportedin patients infected with the H1N1 virus and this correlatedwith worsened outcome.[17] A study from Australia[11] also foundevidence of an IgG2 subclass deficiency in patients with severeH1N1 infections and the IgG2 deficiency was considered to bethe underling risk factor for severity.