Case-fatality rate of SARS-CoV-2 infection during the third and fifth epidemic waves in Spain: Impact of vaccination

INTRODUCTION: During the first and second epidemic waves in Spain, the SARS-CoV-2 case-fatality rates (CFRs) showed significant differences between Autonomous Communities (ACs). Comparing CFRs in the third and fifth epidemic waves can provide information on the impact of the different vaccination coverages in the ACs. OBJECTIVE: To evaluate the impact of vaccination on COVID-19 CFRs in the third and fifth epidemic waves in Spain, according to sex, age, and AC. METHODS: This work is an observational, descriptive study which uses data on COVID-19 infections, deaths, and vaccinees published by the Spanish Ministry of Health and the regional Health Departments of the ACs. The third epidemic wave was defined as the period from 26th December 2020 to 19th April 2021, and the fifth wave, from 19th July to 19th September 2021. The CFRs (deaths per 1000 infected [‰]) were calculated according to sex, age group, and AC. The standardized case-fatality ratio (SCFR) was adjusted for age and sex for each wave. We estimated the correlation between CFRs and their change between the two epidemic waves with the vaccination coverages reached at the beginning of the fifth wave. RESULTS: The CFR in the fifth wave (5.7‰) was lower than in the third wave (16.5‰). In addition, the CFR in both waves was significantly higher in men than in women, and in older people than in younger ones. A decrease in the CFR between both waves was only observed in those older than 49. A strong direct and positive correlation (R(2)a = 0.8399) was found between vaccination coverage by age group and decrease in CFR between both epidemic waves. Significant differences were seen between ACs in the two waves, as regards both CFRs and SCFRs. When comparing ACs, a direct correlation was observed between vaccination coverage and CFRs in the fifth wave, and also – although weak – between vaccination coverage and decrease in CFR between both waves. CONCLUSION: The CFR significantly decreased in Spain between the third and the fifth epidemic waves in population aged 50 or older, probably due to the high vaccination coverage in that age group. Differences were observed between CFRs and SCFRs between ACs that are not explained by the differences in vaccination coverage, suggesting the need for further research and evaluation.