Covid-19 no Brasil (2020-2024): vigilância epidemiológica, desigualdades e impacto da vacinação na população geral e idosa

Abstract

The covid-19 pandemic revealed deep structural inequalities in Brazil, with heterogeneous impacts across regions, social groups, and age strata. This thesis comprises two complementary researches: a nationwide analysis of the evolution of covid-19 in Brazil between 2020 and 2024, and a focused investigation on the elderly population, identified early on as the most vulnerable group. Chapter 1 aimed to characterize the epidemiological patterns of Severe Acute Respiratory Syndrome (SARS) caused by covid-19, considering regional, sociodemographic, clinical, genomic, and vaccination-related aspects. Using large-scale national public databases, multivariate analyses and Kaplan-Meier survival models were applied. Three distinct epidemic waves were identified, with the second being the most lethal. The overall case fatality rate was 33.6%, with higher proportions among individuals living in regions with lower HDI, lower education levels, Black or Multiracial groups, and those unvaccinated. Booster vaccine doses were significantly associated with reduced mortality risk and increased survival. Chapter 2 explored the elderly population (aged 60 years and older), who accounted for nearly half of all severe PCR-confirmed cases in the study period. The case fatality rate among the elderly was 47.6%, increasing with age and reaching 68.6% among centenarians. Older adults with three or more comorbidities had the worst outcomes, regardless of vaccination status. However, the first and second booster doses were associated with markedly improved survival, even among those with multiple risk factors. Male sex, low education, Black or Multiracial racial groups, peri-urban/rural residence, and municipalities with lower HDI were significantly associated with higher mortality. Kaplan-Meier curves showed that booster vaccination mitigated the negative effect of multimorbidity on survival. Social inequalities persisted throughout the five-year period, despite expanded vaccine coverage. This thesis highlights the need for pandemic preparedness strategies that address the complex interplay of biological, social, and structural determinants. Continuous surveillance, timely vaccine deployment, and equity-oriented public policies are essential, with a focus on the elderly population—the most severely impacted group.