1. Covid-19 Data Explorer Our World in Data. https://ourworldindata.org/explorers/coronavirus-data-explorer
2. Covid-19 data: tracking covid-19 excess deaths across countries. Economist . www.economist.com/graphic-detail/coronavirus-excess-deaths-tracker
3. Over 53000 doctors in our country have been vaccinated against covid-19. [Bulgarian] Bulgarian Medical Association. 27 July 2021. https://blsbg.com/bg/nad-53-na-sto-ot-meditsite-u-nas-sa-vaksinirani-sreshchu-covid-19_p10531.html
4. Serbia covid-19 dashboard. https://covid19.rs/homepage-english
5. Holt E . Covid-19 vaccination among Roma populations in Europe. Lancet 2021;2:E289