Krumova S, Golkocheva-Markova E, Angelova S, et al. Dried Blood Spots as a Clinical Samples for Laboratory Diagnosis and Surveillance of Vaccine-Preventable Diseases in Bulgaria. ASRJETS-Journal. 2019;51(1):183-191. Accessed September 18, 2025. https://asrjetsjournal.org/American_Scientific_Journal/article/view/4611