A three- to five-year course of allergen immunotherapy remains effective for more than five years after discontinuation of the shots, suggest the results of a survey of immunotherapy patients in Tennessee.

A couple of trials have shown that “grass pollen immunotherapy worked for at least three years after it was discontinued,” for those who had three to five years of treatment, Dr. John M. Fahrenholz told Reuters Health. But limited data are available on the potential enduring benefit of immunotherapy beyond five years, he added.

To investigate, Fahrenholz and colleagues, from Allergy and Asthma Specialists, PLLC, in Nashville, Tennessee, compared the return of allergy symptoms in two groups of patients - 126 had completed immunotherapy one to four years prior and 167 had completed immunotherapy five to 12 years prior.

He presented his group’s findings Tuesday during the 61st annual meeting of the American Academy of Allergy Asthma and Immunology.

“We did not find any major differences in these two [group] - those being off shots one to four years and those being off shots five or more years - with regards to the return of symptoms,” Fahrenholz said.

In the more recently treated group, the average symptom score before immunotherapy, at the completion of immunotherapy, and at present was 8.48, 2.96, and 3.97, respectively. In the second group, the score for these time periods was 8.26, 2.94, and 3.95.

The main conclusion is that allergen immunotherapy appears to have “enduring benefit that did not show signs of waning anymore if you’ve been off them several more years compared to just a few years,” Fahrenholz said. “Certainly some symptoms increase - but for the most part, people had long-lasting benefit.”