Measles and public health: an integrative approach

Measles, once considered under control in many high-income countries, has experienced a notable resurgence in recent years due to declining vaccination rates, increased vaccine hesitancy, and gaps in public health preparedness. This study provides an overview of the current measles outbreaks in two socio-culturally distinct realities, both facing a challenging epidemiological situation, i.e., the Region of the Americas and Italy, the European country most impacted after Romania. The aim is to understand transmission dynamics and identify factors contributing to outbreak severity.

Epidemiological data show that Canada experienced an unprecedented increase in measles incidence, particularly in Ontario and Alberta, where spatial modelling revealed relative risks greater than 30 in high burden areas (i.e., the estimated likelihood of measles occurrence in these areas was more than 30 times higher than the national average, based on Bayesian spatial modeling). In Mexico, the epidemic was highly localised, with over 90% of cases and all but one death concentrated in the state of Chihuahua. In the United States, 89% of cases were linked to epidemic outbreaks, with Texas showing significant spatial clustering and daily growth rates of over 4% in high-risk counties. In Italy, the 2024 outbreak marked a significant increase in measles cases compared to previous years, primarily affecting unvaccinated individuals. Over 50% of those affected required hospitalization, and major urban regions such as Lazio and Lombardy experienced sustained transmission. An initial phase of exponential growth (66% monthly) was followed by a plateau, with no significant decline observed, underlining delays in containment and persistent immune deficiencies. From genetic point of view, the study revealed the predominance of genotype D8, known for sustained global circulation, suggesting a single transmission chain behind the recent outbreaks. Phylogenetic analysis showed no significant intra-genotypic diversification, suggesting that the outbreak likely originated from a single introduction event followed by rapid, localized transmission. This limited genetic variation is consistent with a short transmission window and the absence of strong evolutionary pressure.

The outbreaks in the United States and Italy, despite differences in healthcare systems and sociopolitical contexts, reveal common underlying issues. In the U.S., the epidemic was characterized by clusters of unvaccinated individuals in certain communities, while Italy faced challenges due to gaps in routine immunization programs and delays in responding to the outbreak. Both outbreaks illustrate the devastating impact of under-vaccination, inadequate surveillance, and the spread of misinformation on public health. Our results contribute to a deeper understanding of the dynamics of measles recurrence, providing a solid basis for science-based prevention and control measures. Furthermore, the study emphasises the importance of continuous and integrated surveillance to detect emerging or divergent strains at an early stage.

Not applicable.