Vaccination Status and Number of Vaccine Doses Are Independently Associated with the PaO₂/FiO₂ Ratio on Admission in Hospitalized COVID-19 Patients

Introduction: Coronavirus Disease-19 (COVID-19) vaccines reduce the risk of severe disease and mortality. However, the association between vaccination status and number of doses and the PaO2/FiO2 ratio, a clinical measure of hypoxemia associated with an increased risk of intensive care treatment and mortality, has not been investigated. Methods: We retrospectively assessed a consecutive series of 116 patients admitted to hospital with a primary diagnosis of COVID-19 between January and April 2022. Demographic, clinical, and laboratory data were collected within 24 h from admission. Results: There was a significant positive relationship between the number of vaccine doses and the PaO2/FiO2 ratio (r = 0.223, p = 0.012). This association remained significant after adjusting for confounders. Vaccinated patients had significantly higher PaO2/FiO2 ratios than the unvaccinated (median: 250; IQR: 195–309 vs. 200; IQR: 156–257, p = 0.013). Conclusion: These results highlight the importance of the number of vaccine doses received in reducing the degree of hypoxia on admission in hospitalized COVID-19 patients.