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 the ECDC report from 16th February 2024 “Measles on the rise in the EU/EEA: considerations for public health response”, urgent action is required to address the increasing spread of measles and insufficient vaccination coverage across the EU. The main objective of the present re-search is a comparative analysis of measles outbreak risk in two neighboring countries with intensive economic relations - Bulgaria and Romania. Our research is part of a larger project for measles outbreak risk assessment in Bulgaria’s neighboring countries to gain broader in-sight on the potential threats in the near future. Methods Data from a 50-year period was collected on immunization coverage and demographic dynamics in Bulgaria and Romania. A mathematical model is applied to estimate the immunization coverage and demographic parameters on yearly basis. This allows us to calculate with satisfactory precision the accumulation of susceptible persons tracing at least 20 years back in the history. The core of the model is the calculation of an annual Risk Index defined as the ratio of all susceptible individuals to the total population. Results The Risk Index curves for measles outbreak in Bulgaria and Romania were 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 are also alarming after 2016. 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 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. An important consideration is that the vaccination coverage should be simultaneously monitored with the demography, which may be missed even by professionals.