Risk Analysis of Measles Outbreaks in Bulgaria and Romania for the Period 2000 to 2023: A Comparative Study.

Purpose: Measles is a highly contagious but vaccine-preventable infectious disease. According to health authorities such as the ECDC (20240, urgent action is required to address the increasing spread of measles and insufficient vaccination coverage across the EU. The main objective of the present research is a comparative analysis of measles outbreak risk in two neighbouring countries with intensive economic relations and similar socio-economic challenges-Bulgaria and Romania. This research aims to deliver results on measles outbreak risk assessment in Bulgaria's neighbouring countries to gain broader insight on the potential threats faced regionally and globally.

Methods: Data from a 50-year period was collected on immunization coverage and demographic dynamics in Bulgaria and Romania. The main objective of the paper is the calculation of an annual Risk Index defined as the ratio of all susceptible individuals to the total population. A mathematical model is applied to estimate the immunization coverage and demographic parameters on an annual basis. This allows us to calculate with satisfactory precision the accumulation of susceptible persons tracing at least 20 years back in the history, needed for the calculation of an annual Risk Index.

Results: The Risk Index curves for measles outbreak in Bulgaria and Romania are calculated for the period 2000 to 2023. The Risk Index curve for Bulgaria reveals a concerning increase after 2015, with particularly alarming values projected for 2017 and later. The results of the Risk Index for Romania after 2016 are also concerning. In 2023, the Risk Index for Bulgaria hits 7.55%, whereas in Romania it hits 8.1%.

Conclusion: Comparing the findings from the Risk Index to the real data from measles outbreaks for two neighbouring countries-with similar socio-demographic challenges-shows that the Risk Index is a good indicator for risk of measles outbreak. It can help the health authorities to forecast potential measles outbreaks - alongside vaccination coverage, demographic factors should also be considered when monitoring public health.