# A national population-based study of mortality and risk factors in COVID-19-hospitalized patients in Spain (2020–2021)

## TL;DR

This study analyzed how vaccination impacted in-hospital mortality and risk factors for hospitalized COVID-19 patients in Spain from 2020 to 2021.

## Contribution

The study provides population-level evidence on the impact of vaccination on in-hospital mortality and identifies consistent risk factors across time.

## Key findings

- In-hospital mortality decreased by 29% during the vaccination period compared to the prevaccination period.
- Age was the strongest risk factor, with mortality rising from 0.8% in 18–39-year-olds to 31.7% in those ≥80 years.
- Female sex and dyslipidemia were protective factors against in-hospital mortality.

## Abstract

The study aimed to analyze in-hospital mortality (IHM) among all COVID-19 patients hospitalized in Spain between March 1, 2020, and December 31, 2021, and to compare two distinct periods: the prevaccination period (March 1, 2020, to January 31, 2021) and the vaccination period (February 1, 2021, to December 31, 2021). The objective was to assess the impact of vaccination on IHM and identify associated risk factors, using data from Spain’s national hospitalization registry.

This retrospective analysis used data from the Spanish National Surveillance System for Hospital Data. The primary outcome was in-hospital mortality (IHM). Multivariate logistic regression identified risk factors across the overall study period, as well as during the prevaccination and vaccination periods. Risk factors included age (in 20-year intervals), sex, comorbidities (e.g., hypertension, diabetes, chronic kidney failure, obesity, neurodegenerative disorders, and others), and admission to the intensive care unit.

A total of 524,314 COVID-19 hospitalizations were recorded in Spain, with 329,690 during the prevaccination period and 194,624 during the vaccination period. Hospitalization rates dropped from 697/100,000 people to 411/100,000, and in-hospital mortality (IHM) decreased from 16.2 to 11.5% (adjusted odds ratio [AOR]: 0.71, 95% CI: 0.70–0.73, p < 0.001). IHM rose with age, from 0.8% in patients aged 18–39 to 31.7% in those ≥80 years (p < 0.001), but significant decreases were observed across all age groups after vaccination, especially in those ≥80 years (AOR: 0.76, 95% CI: 0.75–0.79, p < 0.001). Risk factors for IHM remained consistent, with leukemia, neoplasm, and lymphoma posing the highest risks, while female sex (AOR: 0.75, 95% CI: 0.74–0.77, p < 0.001) and dyslipidemia (AOR: 0.85, 95% CI: 0.32–0.86, p < 0.001) were protective factors.

During the vaccination period, the risk of in-hospital mortality (IHM) was 29% lower than in the prevaccination period, after adjusting for sex, age, and comorbidities. This reduced risk was observed across sexes, age groups, and comorbidities. The risk factors for IHM remained consistent between the two periods, with age as the main risk factor, while female sex and dyslipidemia were identified as protective factors.