Vitamin D, in addition to its classical functions in bone homeostasis, has a modulatory and regulatory role in multiple processes, including host defense, inflammation, immunity, and epithelial repair. Patients with respiratory disease are frequently deficient in vitamin D, implying that supplementation might provide significant benefit to these patients. Respiratory viral infections are common and are the main trigger of acute exacerbations and hospitalization in children and adults with asthma and other airways diseases. Respiratory monocytes/macrophages and epithelial cells constitutively express the vitamin D receptor. Vitamin D, acting through this receptor, may be important in protection against respiratory infections. Whether the in vitro findings can be translated into a substantial in vivo benefit still remains uncertain. Here we review the in vitro data on the role of vitamin D in antiviral innate immunity, the data concerning the deficient levels of vitamin D in lung diseases, and the in vivo role of supplementation as protection against respiratory viral infections in healthy individuals and in patients with chronic respiratory diseases. Finally, we suggest ways of improving the effectiveness of vitamin D as an adjuvant in the prevention and treatment of acute respiratory infections.

Immunocompromised individuals such as chronic lymphocytic leukemia (CLL) patients are at risk of impaired immune responses to vaccination. The objective of our study was to evaluate SARS-CoV-2-specific antibody responses in CLL patients, after the first, second and third doses of the BNT162b2 and mRNA-1273, and after a single dose for patients with confirmed prior COVID-19. Five hundred and thirty patients were included in the study. Patients received 2 doses at a 4-week interval, and a third dose if seronegative after the second dose. Response rate was 27% post-dose 1 and 52% post-dose 2. Post-dose 2 treatment-naïve patients had the highest response rate (72%) followed by patients previously treated by chemoimmunotherapy (60%). Among patients on therapy, patients on BTKi alone (22%) or in combination with anti-CD20 monoclonal antibodies or venetoclax (0%) had the poorer response rate whereas patients on venetoclax monotherapy achieved a significantly higher response rate (52%). A multivariate analysis identified as independent predictors of the absence of seroconversion: age >65 years, ongoing CLL treatment and gamma-globulins ≤6g/L. Post-dose 2 seronegative patients had a global post-dose 3 response rate of 35%. This study provides an argument for the use of a third dose and for prophylactic SARS-CoV-2 neutralizing monoclonal antibodies.