Do Allergies Stay Gone After Immunotherapy? Data | Curex

Quick Answer

Allergies do stay significantly reduced after completing immunotherapy — but only if you finish at least 3 years. The Marogna 15-year study (n=78) showed benefits lasting 7 years after a 3-year course, 8 years after 4 years, and 8 years after 5 years. Two years is definitively insufficient — the GRASS trial (Scadding 2017, JAMA) confirmed that 2-year courses do not produce lasting benefit.

Quick Facts

Detail	Info
Benefit duration after 3 years SLIT	7 years (Marogna 2010, n=78)
Benefit duration after 4–5 years	8 years (Marogna 2010)
2-year course outcome	No lasting benefit — GRASS trial (Scadding 2017, JAMA)
Large-scale confirmation	REACT study (n=92,048): both SCIT and SLIT sustained 7–9 years (Fritzsching 2022, Lancet)
Non-responder rate	20–30% do not respond regardless of duration (Gotoh 2017)
3-year drops total cost	$4,200–5,940; 5-year total = $6,000–8,500 (2026)

"Will My Allergies Come Back After I Stop Treatment?"

Three years of daily drops. You finally sleep through the night without congestion. Spring arrives and you barely notice. Then your prescription ends, and a single thought takes root: what if this all reverses?

You picture next April — eyes swelling shut again, tissues piled on your nightstand, reaching for the antihistamine you thought you'd outgrown. The improvement felt gradual enough that you're not even sure when it started, which makes you wonder how you'd know when it stops.

Why This Happens — The Immune Memory Timeline

Step 1 — Your immune system builds lasting tolerance markers. At 2 years post-treatment, 67% of patients maintained regulatory T cells (Tregs), 83% had persistent IgG4 blocking antibodies, and 60% kept IgG4 levels above pre-treatment baseline (Suárez-Fueyo 2014/2018). These are the immune cells and antibodies that prevent allergic reactions.

Step 2 — Duration of treatment determines duration of benefit. The Marogna 15-year follow-up tracked patients who completed 3, 4, or 5 years of SLIT. Benefits persisted 7 years after a 3-year course, 8 years after 4 years, and 8 years after 5 years. Four and five years produced nearly identical long-term outcomes, suggesting diminishing returns beyond year 4.

Step 3 — Large-scale data confirms the pattern. The REACT study (Fritzsching 2022, Lancet) followed 92,048 patients and found both SCIT and SLIT sustained benefits for 7–9 years. This is the largest real-world immunotherapy study ever conducted and validates what smaller trials showed.

What To Do Next

Step 1 — Confirm you've reached the 3-year minimum. If you're considering stopping, count your actual treatment months. Two years is definitively insufficient — the GRASS trial and Renand 2018 both confirmed this. Every month between year 2 and year 3 adds meaningful long-term protection.

Step 2 — Assess your response before deciding on year 4 or 5. If you've had clear improvement by 12 months, continuing to year 3 is strongly supported. Years 4 and 5 add approximately 1 additional year of post-treatment benefit (8 vs 7 years). Discuss with your provider whether that tradeoff justifies the additional cost.

Step 3 — Track your specific allergen triggers post-treatment. After completing treatment, monitor symptoms during your worst allergy season for the first 2 years. If symptoms return, retreatment may be an option — one study reported that a second course induced benefit more rapidly, though this comes from a single study without quantified data.

Take the free 3-minute allergy quiz →

When Stopping Early Makes Sense

Completing less than 3 years produces significantly reduced long-term benefit. But stopping IS sometimes the right call: if you're planning pregnancy (conservative approach), starting immunosuppressive medication, or managing a severe acute illness. About 20–30% of patients are non-responders regardless of duration (Gotoh 2017). If you've seen zero improvement after 6–12 months, more years of the same treatment won't fix non-response — reassess with your provider rather than assuming longer treatment will eventually work.

New sensitizations tell another important story: in the Marogna study, 100% of untreated patients developed new allergen sensitivities over 15 years, compared to only 21% of the 3-year group, 12% of 4-year, and 11% of 5-year. Completing treatment doesn't just treat current allergies — it dramatically reduces new ones.

Related Issues to Check

What happens if you stop immunotherapy early? — The specific biological consequences of stopping at 1 year vs 2 years, and why 7% completion rates mean most people face this question.
How long until allergy drops work? — Understanding the month-by-month timeline helps calibrate expectations and distinguish non-response from normal early-treatment phases.
Allergy drops cost per month — Knowing the 3-year vs 5-year total cost helps you plan financially for the minimum duration needed for lasting benefit.

Frequently Asked Questions

Is 2 years of immunotherapy enough? No. The GRASS trial (Scadding 2017, JAMA) definitively showed that 2 years of SLIT does not produce lasting clinical benefit. Three years is the evidence-based minimum.

How long do benefits last after 3 years of drops? The Marogna 15-year follow-up showed benefits lasting approximately 7 years after a 3-year course. The REACT study (n=92,048) confirmed 7–9 year sustained benefit for both drops and shots (Fritzsching 2022, Lancet).

Is 5 years better than 3 years? Marginally. Marogna showed 8 years of benefit after 5 years vs 7 years after 3 years. Four years produced the same 8-year benefit as 5 years, suggesting year 4 may be the practical sweet spot.

Can I restart immunotherapy if allergies return? One study (Marogna) reported that a second course "induced benefit more rapidly" — but this is a single study without quantified data. Retreatment is an option, but robust data on second-course timelines is limited.

What percentage of people don't respond at all? Approximately 20–30% of patients are non-responders regardless of treatment duration (Gotoh 2017). Non-response should be assessed at 6–12 months, not after completing the full course.

Do children maintain benefits as long as adults? Monosensitized children maintained benefits for approximately 7 years. Polysensitized children saw benefit wane starting from year 5 post-treatment (Cui 2019). Multiple allergies may require longer initial treatment in pediatric patients.

Last reviewed: March 2026 · Sources verified against current data

Medically reviewed by Dr. Chet Tharpe, MD · March 2026

Take the Next Step

If you're weighing whether to start, continue, or stop immunotherapy, knowing your specific allergen profile helps determine the right duration. A 3-minute quiz identifies your triggers and severity.