Co-Seasonal Initiation of Allergen Immunotherapy: A Systematic Review

Rationale: It is unclear if allergen immunotherapy (AIT) can be safely initiated during pollen season (co-seasonal initiation [CSI]) because of a potential increased risk of systemic reactions. Publications reporting the safety of subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT) CSI were systematically reviewed to validate or invalidate the perception of increased safety risk.

Methods: PubMed, EMBASE, Ovid, LILACS, and Cochrane Library databases were searched without limits for studies of any design reporting SCIT or SLIT CSI for pollen allergen. Congress abstracts were included.

Results: Nineteen eligible studies were identified; 8 SCIT (n=947 subjects total; n=340 double-blind placebo-controlled [DBPC]) and 11 SLIT (n=2,668 subjects total; n=565 DBPC). Study characteristics and safety reporting were heterogeneous. No epinephrine administrations were reported. Discontinuation frequencies were ≤5.6% and ≤10% with SCIT and SLIT CSI, respectively. In DBPC SCIT studies, systemic allergic reaction frequency was ≤7.1% with CSI and ≤6.9% with placebo; no systemic allergic reactions with CSI were reported in retrospective studies. In SCIT studies, serious treatment-related adverse event (TRAE) frequency with CSI ranged from 0%−2%; besides local reactions no severe AEs were reported. In DBPC SLIT studies, systemic allergic reaction frequency was ≤2% with CSI and ≤0.55% with placebo; no systemic allergic reactions with CSI were reported in a retrospective study. Overall, 2 serious TRAEs with SLIT CSI were reported. Severe AE frequency in SLIT studies was ≤7.7% for CSI and ≤11.9% with placebo or non-CSI.

Conclusions: No increased safety signal was observed with SCIT or SLIT CSI; however, additional data with standardized regimens and doses are needed.