Allergy Shots Effectiveness: Per-Allergen Data Table

The Cochrane meta-analysis by Calderón MA et al. (2007, CD001936) aggregated 51 double-blind, placebo-controlled RCTs involving 2,871 patients in seasonal allergic rhinitis and found a pooled symptom SMD of −0.73 (95% CI −0.97 to −0.50) and a medication SMD of −0.57 (95% CI −0.82 to −0.33). Both are statistically significant at P<0.00001. This is a moderate-to-large effect in clinical research terms. For asthma, Abramson MJ et al. (Cochrane 2010, CD001186) found an NNT of 3 across 88 SCIT trials. Critically, these are aggregate estimates — per-allergen effectiveness varies from near-100% for Hymenoptera venom to very thin evidence for mountain cedar and non-Alternaria molds. No single number accurately describes allergy shot effectiveness across all allergens.

Hymenoptera venom produces the most dramatic effect — subsequent systemic sting reactions in 2.7% of VIT-treated patients versus 39.8% untreated (Boyle 2012 Cochrane). Grass and ragweed have the strongest aeroallergen RCT base: grass produces approximately 80% medication-score reduction (Walker 2001) with durable remission after stopping (Durham 1999). Cat SCIT produces approximately 62% symptom reduction on natural challenge (Varney 1997). Alternaria mold achieves 63.5% combined symptom-score reduction by year 3 in children (Kuna 2011). Birch evidence is moderate (~40% symptom, ~50% medication reduction per Bødtger 2002). Mountain cedar has no robust conventional SCIT RCT. Non-Alternaria molds (Cladosporium, Aspergillus) have essentially no controlled evidence. Extrapolation from the Cochrane SMDs to these thin-evidence allergens is not scientifically supported.

Yes — effectiveness follows a predictable temporal pattern. Build-up (approximately 26–28 weekly injections over 6 months) is about reaching the effective maintenance dose, not about symptom control — Cox 2011 PP3 characterizes this phase as producing 'partial and unreliable' relief. Most patients notice clear improvement between months 6 and 12. The largest and most consistent symptom and medication reductions accrue in years 2–3, as documented in Walker SM et al. (JACI 2001) and Durham SR et al. (NEJM 1999). Maximum disease-modification effect (durable post-treatment remission) requires completing a 3–4 year course. Courses shorter than approximately 2 years produce weaker durability per Durham 1999.

Four factors can reduce effectiveness: (1) Multi-allergen-vial dilution — mixing many allergens in one vial can dilute each component below its effective maintenance dose and can cause proteolytic interactions (mold enzymes degrading other extracts); US practice frequently uses multi-allergen mixes, unlike European single-allergen trials. (2) Incorrect sensitization match — if the extract targets a bystander allergen rather than the dominant sensitization, the biological effect is reduced. (3) Short course duration — courses under 2 years are associated with weaker durability and higher relapse. (4) Dropout — 23.9% of US starters never return after their first injection (Tkacz 2021), missing the dose-response curve entirely. Comorbid poorly-controlled asthma also limits both safety and effectiveness.

Cat SCIT is supported by European RCT evidence. Alvarez-Cuesta E et al. (JACI 1994;93:556–566) used monoclonal antibody-standardized cat extract and found significant improvement in combined symptom-medication score. Varney VA et al. (Clin Exp Allergy 1997;27:860–867) documented approximately 62% symptom reduction on natural cat-room challenge. The extract used is FDA-standardized cat hair extract (Greer license #308, 10,000 BAU/mL) targeting the major allergen Fel d 1. Cat SCIT does not make cat ownership safe — allergen avoidance remains important even during treatment. The ~62% figure refers to controlled natural challenge conditions and may not translate exactly to real-world household cat exposure.

Venom immunotherapy (VIT) is the most effective form of immunotherapy in clinical medicine. Boyle RJ et al. (Cochrane 2012, PMID 23076950) found subsequent systemic sting reactions in 2.7% of treated patients versus 39.8% of untreated controls — a risk ratio of 0.10 (95% CI 0.03–0.28). Golden DBK et al. (JACI 2005;115:439–447) documents that VIT prevents systemic reactions in more than 95% of treated patients overall: single-vespid VIT 85–90% effective; honeybee VIT 75–85% effective. Protection commonly persists after stopping a 3–5 year course, though relapse risk is higher with elevated baseline serum tryptase and with honeybee venom. Hunt KJ et al. (NEJM 1978;299:157–161) established the landmark controlled trial demonstrating VIT efficacy. Patients are still advised to carry an epinephrine auto-injector even after completing treatment.