[COVID-19 as a syndemic: a theoretical model and foundations for a comprehensive approach in health]

This essay aims to present and discuss the theoretical framework for the COVID-19 syndemic. The first part presents the foundations and principles of syndemic theory. For the purposes of this essay, syndemic was defined as a process of synergic interaction between two or more diseases, in which the effects are mutually enhanced. We discussed the three principal typologies of syndemic interaction: mutually causal epidemics; epidemics interacting synergically; and serial causal epidemics. In the second part, COVID-19 is analyzed as a syndemic resulting from the interaction between various groups of diseases and the socioeconomic context. The theoretical model considered the interaction between COVID-19 and chronic noncommunicable diseases, infectious and parasitic diseases, and mental health problems. The essay addressed how social iniquities and conditions of vulnerability act at various levels to increase the effect of COVID-19 and other pandemics. The last section discusses the need for comprehensive, multisector, and integrated responses to COVID-19. A model for intervention was presented that involves the patient care and socioeconomic dimensions. In the sphere of patient care, the authors defend the structuring of strong and responsive health systems, accessible to the entire population. The economic and social dimension addressed the issue of reclaiming the ideals of solidarity, the health promotion strategy, and emphasis on social determinants of health. In conclusion, the lessons learned from the syndemic approach to COVID-19 call on government and society to develop policies that link clinical, sanitary, socioeconomic, and environmental interventions.