Luković, Milica, and Jovan Nićiforović. “INCREASED DEMANDS FOR NATURAL IMMUNO- BOOSTERS IN SELECTED TOURISM AREAS”. Tourism International Scientific Conference Vrnjačka Banja - TISC 6, no. 1 (June 3, 2021): 366-381. Accessed October 7, 2025. http://www.tisc.rs/proceedings/index.php/hitmc/article/view/409.