ADULT VACCINATION ATTITUDES AND UPTAKES IN BULGARIA
A Cross-Sectional Study of Influenza, COVID-19, and Pneumococcal Vaccines
DOI:
https://doi.org/10.58395/aj75k003Keywords:
vaccination, Influenza, COVID-19, Streptococcus pneumoniae, attitudes, practices, hesitancyAbstract
Background: Vaccination rates for adults in Eastern Europe are still not satisfactory, especially for flu, COVID-19, and pneumococcal disease. There isn't much information available about how many Bulgarian adults get vaccinated and what factors affect their decision to do so. This study sought to evaluate vaccination coverage, attitudes, and barriers concerning influenza, COVID-19, and pneumococcal vaccines among hospitalised Bulgarians.
Methods: A cross-sectional study was conducted from June to September 2023, with 222 individuals hospitalised in Plovdiv, Bulgaria. A structured questionnaire assessed sociodemographic factors, comorbidities, immunisation practices, and perceptions regarding adult immunisations. We employed SPSS v25 for descriptive statistics and comparative analyses, including the Mann–Whitney U test and the Z-test. A p-value below 0.05 was considered statistically significant.
Results: The average age of participants was 58 years, with 63.5% identifying as female and 55.9% disclosing at least one comorbid health condition. 52.2% of individuals received at least one of the three immunisations; however, the number of individuals who received each specific vaccine was minimal. Twenty-three point three per cent of participants with comorbidities and eighteen point four per cent of those without comorbidities indicated they had the influenza vaccine in the prior season (p=0.363). Approximately 5% of individuals were immunised against pneumococcal illness, and fewer than 20% were aware of it. The apprehension of adverse effects was a significant concern, particularly for individuals with pre-existing health issues. The absence of a physician's recommendation significantly contributed to the low uptake of the pneumococcal vaccine (45.2% vs. 28.6%, p=0.011). Approximately one in four respondents expressed belief in COVID-19 conspiracy theories. Respondents indicated that they were more likely to trust public institutions and general practitioners for information.
In conclusion, Bulgaria's adult vaccination rates are insufficient, particularly for pneumococcal disease. Concerns regarding safety and the lack of recommendations from medical professionals are two significant issues. To increase adult vaccination rates in the present situation, it is essential to improve collaboration among healthcare providers and the dissemination of public health messaging.
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References
1. Troeger C.E., Blacker B.F., Khalil I.A., Zimsen S.R.M, Albertson S.B, Abate D, et al. Mortality, morbidity, and hospitalisations due to influenza lower respiratory tract infections, 2017: An analysis for the Global Burden of Disease Study 2017. Lancet Respir. Med. 2019, 7, 69–89. https://doi.org/10.1016/S2213-2600(18)30496-X DOI: https://doi.org/10.1016/S2213-2600(18)30496-X
2. Torres, A, Cillóniz, C, Blasi F, Chalmers J.D., Gaillat J, Dartois N, et al. Burden of pneumococcal community-acquired pneumonia in adults across Europe: A literature review. Respir. Med. 2018, 137, 6–13. https://doi.org/10.1016/j.rmed.2018.02.007. DOI: https://doi.org/10.1016/j.rmed.2018.02.007
3. Lafond KE, Porter RM, Whaley MJ, Suizan Z, Ran Z, Aleem MA, et al. Global burden of influenza-associated lower respiratory tract infections and hospitalizations among adults: A systematic review and meta-analysis. PLoS Med. 2021;18(3):e1003550. https://doi.org/10.1371/journal.pmed.1003550. DOI: https://doi.org/10.1371/journal.pmed.1003550
4. Kobayashi M, Pilishvili T, Farrar JL, Leidner AJ, Gierke R, Prasad N, et al. Pneumococcal Vaccine for Adults Aged ≥19 Years: Recommendations of the Advisory Committee on Immunization Practices, United States, 2023. MMWR Recomm Rep. 2023;72(3):1-39. https://doi.org/10.15585/mmwr.rr7203a1. DOI: https://doi.org/10.15585/mmwr.rr7203a1
5. Reyes LF, Conway Morris A, Serrano-Mayorga C, Derde LPG, Dickson RP, Martin-Loeches I. Community-acquired pneumonia. Lancet. 2025;406(10517):2371-2388. https://doi.org/10.1016/S0140-6736(25)01493-X. DOI: https://doi.org/10.1016/S0140-6736(25)01493-X
6. Said MA, Johnson HL, Nonyane BA, Deloria-Knoll M, O'Brien KL; AGEDD Adult Pneumococcal Burden Study Team et al. Estimating the burden of pneumococcal pneumonia among adults: a systematic review and meta-analysis of diagnostic techniques. PLoS One. 2013;8(4):e60273. https://doi.org/10.1371/journal.pone.0060273. DOI: https://doi.org/10.1371/journal.pone.0060273
7. HCSP. Vaccination des Personnes Immunodéprimées ou Aspléniques. In Recommandations Actualisées; Haut Conseil de la SantéPublique: Paris, France. Available online: http://www.hcsp.fr/explore.cgi/avisrapportsdomaine?clefr=504.
8. ECDC Technical report Seasonal influenza vaccination recommendations and coverage rates in EU/EEA member states, 2023. [Last accessed 23 February 2026]. Available online: https://www.ecdc.europa.eu/sites/default/files/documents/Seasonal-flu-vacc-recs-coverage-rates-EU-EEA.pdf
9. Tan L. Adult vaccination: Now is the time to realize an unfulfilled potential. Hum Vaccin Immunother. 2015;11(9):2158-66. https://doi.org/10.4161/21645515.2014.982998. DOI: https://doi.org/10.4161/21645515.2014.982998
10. Blank PR, van Essen GA, Ortiz de Lejarazu R, Kyncl J, Nitsch-Osuch A, Kuchar EP, et al. Impact of European vaccination policies on seasonal influenza vaccination coverage rates: An update seven years later. Hum Vaccin Immunother. 2018;14(11):2706-2714. https://doi.org/10.1080/21645515.2018.1489948. DOI: https://doi.org/10.1080/21645515.2018.1489948
11. Wyplosz B, Fernandes J, Sultan A, Roche N, Roubille F, Loubet P, et al. Pneumococcal and influenza vaccination coverage among at-risk adults: A 5-year French national observational study. Vaccine. 2022;40(33):4911-4921. https://doi.org/10.1016/j.vaccine.2022.06.071. DOI: https://doi.org/10.1016/j.vaccine.2022.06.071
12. Papazoglou DD, Baretella O, Feller M, Del Giovane C, Moutzouri E, Aujesky D, et al. Cross-sectional study on the prevalence of influenza and pneumococcal vaccination and its association with health conditions and risk factors among hospitalized multimorbid older patients. PLoS One. 2021;16(11):e0260112. https://doi.org/10.1371/journal.pone. DOI: https://doi.org/10.1371/journal.pone.0260112
13. Kumar S, Shah Z, Garfield S. Causes of Vaccine Hesitancy in Adults for the Influenza and COVID-19 Vaccines: A Systematic Literature Review. Vaccines (Basel). 2022;10(9):1518. https://doi.org/10.3390/vaccines10091518. DOI: https://doi.org/10.3390/vaccines10091518
14. Larson HJ, Gakidou E, Murray CJL. The Vaccine-Hesitant Moment. N Engl J Med. 2022;387(1):58-65. https://doi.org/10.1056/NEJMra2106441. DOI: https://doi.org/10.1056/NEJMra2106441
15. Bach AT, Kang AY, Lewis J, Xavioer S, Portillo I, Goad JA. Addressing common barriers in adult immunizations: a review of interventions. Expert Rev Vaccines. 2019;18(11):1167-1185. https://doi.org/10.1080/14760584.2019.1698955. DOI: https://doi.org/10.1080/14760584.2019.1698955
16. Cunningham-Erves J, George W, Sanderson M, Stewart E, Jin SW, Davis J, Brandt HM. Predictors of seasonal influenza and COVID-19 vaccination coverage among adults in Tennessee during the COVID-19 pandemic. Front Public Health. 2024;12:1321173. https://doi.org/10.3389/fpubh.2024.1321173. DOI: https://doi.org/10.3389/fpubh.2024.1321173
17. Sulis G, Basta NE, Wolfson C, Kirkland SA, McMillan J, Griffith LE, Raina P; Canadian Longitudinal Study on Aging (CLSA) Team. Influenza vaccination uptake among Canadian adults before and during the COVID-19 pandemic: An analysis of the Canadian Longitudinal study on Aging (CLSA). Vaccine. 2022;40(3):503-511. https://doi.org/10.1016/j.vaccine.2021.11.088. DOI: https://doi.org/10.1016/j.vaccine.2021.11.088
18. Chen C, Liu X, Yan D, Zhou Y, Ding C, Chen L, et al. Global influenza vaccination rates and factors associated with influenza vaccination. Int J Infect Dis. 2022;125:153-163. https://doi.org/10.1016/j.ijid.2022.10.038. DOI: https://doi.org/10.1016/j.ijid.2022.10.038
19. Zaprutko T, Kremin Y, Michalak M, Bernatoniene J, Zaprutko L, Hudz N, et al. Social Attitude to COVID-19 and Influenza Vaccinations after the Influenza Vaccination Season and between the Second and Third COVID-19 Wave in Poland, Lithuania, and Ukraine. Int J Environ Res Public Health. 2022;19(4):2042. https://doi.org/10.3390/ijerph19042042. DOI: https://doi.org/10.3390/ijerph19042042
20. Achterbergh RCA, McGovern I, Haag M. Co-Administration of Influenza and COVID-19 Vaccines: Policy Review and Vaccination Coverage Trends in the European Union, UK, US, and Canada between 2019 and 2023. Vaccines (Basel). 2024;12(2):216. https://doi.org/10.3390/vaccines12020216. DOI: https://doi.org/10.3390/vaccines12020216
21. Toshkov D. What accounts for the variation in COVID-19 vaccine hesitancy in Eastern, Southern and Western Europe? Vaccine. 2023;41(20):3178-3188. https://doi.org/10.1016/j.vaccine.2023.03.030. DOI: https://doi.org/10.1016/j.vaccine.2023.03.030
22. Eagan RL, Claessens T, Hendrickx G, Larson HJ, Karafillakis E. The state of vaccine confidence among the general public in Eastern Europe and Central Asia. Vaccine. 2025;67:127849. https://doi.org/10.1016/j.vaccine.2025.127849. DOI: https://doi.org/10.1016/j.vaccine.2025.127849
23. Wyplosz B, Grenier B, Roche N, Roubille F, Loubet P, Sultan A, et al. Pneumococcal vaccination at 65 years and vaccination coverage in at-risk adults: A retrospective population-based study in France. PLoS One. 2025;20(8):e0329703. https://doi.org/10.1371/journal.pone.0329703. DOI: https://doi.org/10.1371/journal.pone.0329703
24. Bridges CB, Hurley LP, Williams WW, Ramakrishnan A, Dean AK, Groom AV. Meeting the Challenges of Immunizing Adults. Am J Prev Med. 2015;49(6 Suppl 4):S455-64. https://doi.org/10.1016/j.amepre.2015.08.014. DOI: https://doi.org/10.1016/j.amepre.2015.08.014
25. Hurley LP, Lindley MC, Allison MA, O'Leary ST, Crane LA, Brtnikova M, et al. Physicians' Use of Evidence-Based Strategies to Increase Adult Vaccination Uptake. Am J Prev Med. 2020;59(3):e95-e103. https://doi.org/10.1016/j.amepre.2020.03.020. DOI: https://doi.org/10.1016/j.amepre.2020.03.020
26. Wheeler SG, Beste LA, Overland MK, Wander PL. Interventions in primary care to increase uptake of adult vaccines: a systematic review. J Public Health (Oxf). 2025;47(2):222-231. https://doi.org/10.1093/pubmed/fdaf008. DOI: https://doi.org/10.1093/pubmed/fdaf008
27. Fuller A, Hancox J, Vedhara K, Card T, Mallen C, Van-Tam JSN, Abhishek A. Barriers and facilitators to vaccination uptake against COVID-19, influenza, and pneumococcal pneumonia in immunosuppressed adults with immune-mediated inflammatory diseases: A qualitative interview study during the COVID-19 pandemic. PLoS One. 2022;17(9):e0267769. https://doi.org/10.1371/journal.pone.0267769. DOI: https://doi.org/10.1371/journal.pone.0267769
28. Zhao Y, Du J, Li Z, Xu Z, Wu Y, Duan W, et al. It is time to improve the acceptance of COVID-19 vaccines among people with chronic diseases: A systematic review and meta-analysis. J Med Virol. 2023;95(2):e28509. https://doi.org/10.1002/jmv.28509. DOI: https://doi.org/10.1002/jmv.28509
29. Choi T, Chan B, Grech L, Kwok A, Webber K, Wong J, et al. Factors Influencing COVID-19 Vaccine Hesitancy among Patients with Serious Chronic Illnesses during the Initial Australian Vaccine Rollout: A Multi-Centre Qualitative Analysis Using the Health Belief Model. Vaccines (Basel). 2023; 11(2):239. https://doi.org/10.3390/vaccines11020239. DOI: https://doi.org/10.3390/vaccines11020239
30. Tan LLJ, A review of the key factors to improve adult immunization coverage rates: What can the clinician do? Vaccine, 2018;36(36):5373-5378. https://doi.org/10.1016/j.vaccine.2017.07.050. DOI: https://doi.org/10.1016/j.vaccine.2017.07.050
31. Siciliani L, Wild C, McKee M, Kringos D, Barry MM, Barros PP, et al. Strengthening vaccination programmes and health systems in the European Union: A framework for action. Health Policy, 2020; 124(5):511-518. https://doi.org/10.1016/j.healthpol.2020.02.015. DOI: https://doi.org/10.1016/j.healthpol.2020.02.015
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Copyright (c) 2026 Vanya Rangelova, Nevena Ivanova, Ani Kevorkyan, Sara Sariyan, Meri Hristamyan (Author)
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