In people with seasonal allergic rhinoconjunctivitis, environmental factors such as daily humidity and daily pollen burden significantly affect the severity of combined symptom and medication score.

In Phase 3 Allergen Immunotherapy (AIT) trials, the basic assumption was that there exists a causal relationship between burden of allergen and symptoms. The interaction between allergen exposure and environmental factors, however, is more complicated.  This analysis reported on a study in which the effects of environmental factors were prospectively considered in order to investigate their influence on AIT outcomes.

The effectiveness of a modified grass subcutaneous immunotherapy product combining microcrystalline tyrosine (MCT) and monophosphoryl lipid A (MPL) as adjuvant system (PQ Grass) vs placebo in volunteers with allergic rhinitis/rhinoconjunctivitis was compared in the exploratory field research. The key outcome ascertained was combined symptom and medication score (CSMS) during peak grass pollen season.

The daily humidity and ozone levels as well as pollen exposure were also estimated. A hierarchical linear mixed model was utilized to design an exploratory analysis that assessed how these environmental factors impacted the key outcome findings using actual cases.

A substantial impact of daily humidity along with the daily pollen burden on CSMS was illustrated. The average CSMS improvement following PQ grass treatment in comparison to placebo raised from 39.5% (on the basis of primary analytic model) without correction for environmental factors to 55.6% with adjustment (observed cases).

Environmental conditions exhibit an effect on CSMS severity. Rectification of these influences by presenting these as covariates can lead to improvements in the primary findings of Phase 3 AIT field studies.