Gaps in allergen immunotherapy administration and SCIT dose-adjustment schedules: need for prospective data

Many abrupt adjustments in the delivery of medical care became necessary owing to the unexpected emergence of the coronavirus disease 2019 pandemic in early 2020. To ensure social distancing and the concomitant requirements for personal protective equipment, practitioners have had to make a myriad of adjustments to continue providing subcutaneous allergen immunotherapy (SCIT). In many practices, SCIT was stopped or administration intervals have been increased, whereas other practices have transitioned some patients to the sublingual administration route.1 Although many locations have recently eased lockdown requirements, this led to a rise in cases in several states, resulting in further lockdowns. Thus, it might very well still take months before our daily routine shall come close to normal again. Learning from historical lessons, the H1N1 influenza “Spanish flu” pandemic lasted 15 months and killed 50 million people. It comprised the following 3 waves: the first (milder) one was in winter-spring 1918; the second wave, in September 1918, was disastrous and deadly, because it coincided with the massive troop gathering and transport of soldiers for World War I and an apparent aggressive mutation of the virus; and the last wave, beginning in 1919, had less severity. Finally, the virus resolved on the development of herd immunity, the ending of the war, and possibly a favorable mutation. Although prevention of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is critical, it is also important that other health concerns are addressed to limit preventable emergencies. Maintaining good health appears to reduce the risk of severe COVID-19 disease. In the context of allergic diseases, SCIT has been reported to reduce symptoms and medication requirements in allergic rhinitis, conjunctivitis, and in patients with immunoglobulin E–dependent asthma, improving the quality of life. Moreover, a case could be made that patients with an allergy might experience some ancillary immunologic benefit in battling an infectious pathogen by being on an effective SCIT dose. Immunotherapy restores the function of dendritic cells and augments the number of active TH1 cells, both enhance innate immunity, which could be important at the start of a SARS-COV-2 infection whose initial mechanism is innate immune suppression, a theory that might be interesting to explore.2 For SCIT to be effective, an optimal target monthly maintenance dose has to be administered. The extended spacing interval of injections, although acceptable from a safety point of view, may result in a diminution of therapeutic efficacy. Thus, as soon as the risk for SARS-CoV-2 transmission and infection can be reduced to levels considered safe by health authorities, it behooves the allergist to return to a maintenance immunotherapy schedule known to be effective. At this moment, there are no data from controlled trials on dose adjustment after gaps in administration. The intention of this article is to review the limited data available and discuss what is needed to answer pressing questions related to resuming SCIT after gaps in therapy.