Subcutaneous immunotherapy may have slight protective effect against COVID-19

Key takeaways:

• Patients on subcutaneous immunotherapy for house dust mite allergy had shorter durations of COVID-19 symptoms.
• Differences in infection rate, symptom duration and hospitalization disappeared after adjustments.

Subcutaneous immunotherapy for house dust mite allergy may slightly protect patients against SARS-CoV-2 infection, especially after the dose-escalation phase, according to a letter published in Clinical and Translational Allergy.

However, vaccination may cover up this effect, Yin Wang, department of allergy, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, and colleagues wrote.

The researchers administered an online WeChat questionnaire to 1,246 patients who were receiving subcutaneous immunotherapy (SCIT) with house dust mite extract for allergic rhinitis (82.4%), allergic asthma (5.3%) or both (12.3%). Average SCIT duration was 1.4 ± 1.3 years.

Also, the researchers sent the questionnaire to 1,078 relatives of these patients who were not receiving any SCIT, including 370 with allergy and 708 who did not have an allergy. The SCIT patients had lower proportions of participants who had at least one dose of the vaccine and who had completed three doses compared with the relatives (P = .0).

SARS-CoV-2 infection rates included 78.6% of patients on SCIT, 81.4% of the allergic relatives and 81.5% of the non-allergic relatives (P < .0001). COVID-19 symptom durations included 5.7 ± 4 days for the SCIT group, 7 ± 4.5 days for the allergic relatives and 7.7 ± 4.4 days for the nonallergic relatives (P = .0).

Hospitalization rates included 0.4% for the SCIT group and 1.73% for the nonallergic relatives (P = .0008), as well as 0.7% for the allergic relatives.

Using two-to-one matching, the researchers adjusted the three groups based on age, sex and vaccination differences to include 396 SCIT patients, 199 allergic relatives and 199 nonallergic relatives.

After matching, infection rates included 78.5% for those on SCIT, 81.9% for allergic relatives and 81.4% for nonallergic relatives. Symptom durations included 7 ± 4.9 for the SCIT group, 6.8 ± 4.5 for the allergic relatives and 7.2 ± 4.7 for the nonallergic relatives (P = .049). Hospitalization rates included 0.7% for the SCIT group, 0.6% for the allergic relatives and 1.2% for the nonallergic relatives (P = .039).

Based on these results, the researchers said that the previously found differences between the groups in infection rates, symptom durations and hospitalizations had disappeared with matching.

Also, patients who had been on SCIT for 6 to 12 months had shorter durations of COVID-19 symptoms than those who had been on SCIT for less than 6 months and those who had been on SCIT for more than 12 months, even though only a quarter of them had finished three doses of COVID-19 vaccines. Further, SCIT duration had no impact on infection or hospitalization rates.

Considering the similar infection rates among the three groups after matching, the researchers said that expression levels of angiotensin converting enzyme 2 or ACE2 may have a minimal impact on omicron infection.

The younger age of the SCIT group before matching, the researchers continued, may have contributed to its slightly lower infection rates.

The researchers further hypothesized that repeated allergen stimulation during SCIT for house dust mites may elicit a strong T-cell response that can cross-react with SARS-CoV-2 and protect these patients from infection.

Compared with SCIT or allergy, the researchers continued, age, sex and vaccination status may be the dominant factors for susceptibility to the omicron strain considering the similar infection rates among the three groups after matching.

Based on these findings, the researchers concluded that SCIT may have a slight protective effect against SARS-CoV-2 infection, particularly after the dose-escalation phase, although vaccination may cover up this effect.