Differential features of the fifth wave of COVID-19 associated with vaccination and the Delta variant in a reference hospital in Catalonia, Spain

Iftimie, S.; Lopez-Azcona, A. F.; Lozano-Olmo, M. J.; Hernandez-Aguilera, A.; Sarra-Moreto, S.; Joven, J.; Camps, J.; Castro, A.

Since the beginning of the COVID-19 pandemic, Spain has suffered five waves of infection, the latter being related to the expansion of the Delta variant and with a high incidence. A vaccination campaign began in December 2020 and by the end of the fifth wave 77.3% of people had been fully vaccinated. Understanding the impact of these new characteristics on COVID-19 is essential for public health strategies. Our objective was to ascertain any differences in the characteristics and outcomes of hospitalized patients during that period compared to previous waves. We found that patients in the fifth wave were considerably younger than before and the mortality rate fell from 22.5 to 2.0%. Admissions to the Intensive Care Unit decreased from 10 to 2%. Patients in the fifth wave had fewer comorbidities, and the age of the patients who died was higher than those who survived. Our results show a marked improvement in patient outcomes in the fifth wave, suggesting success of the vaccination campaign despite the explosion in cases due to the Delta variant.