Epidemiological study on the impact of influenza vaccination on the clinical course of patients with COVID-19 and co-infection by both viruses in Gran Canaria, Spain

Abstract

To analyze the frequency of influenza and SARS-CoV-2 co-infections, as well as the differences in the course of disease (risk of mortality, hospital and intensive care admissions) in patients infected with the SARS-CoV-2 virus in relation to flu vaccination status in the 2021-2022 season. Population-based observational retrospective study in a cohort of 19,850 patients diagnosed with COVID-19 between June 1, 2021 and February 28, 2022 on the island of Gran Canaria. A total of 1,789 patients (9%) diagnosed with COVID-19 had received flu vaccinations. 13,676 people (68.9%) had a full course of COVID-19 vaccinations. In the period between June 1, 2021 and February 28, 2022, 8 cases of flu and COVID-19 coinfection were recorded. Hypertension (18.5%), asthma (12.8%) and diabetes (7.2%) were the most frequent comorbidities. There were 147 deaths (0.7%). Older patients ([OR] 1.11 95% CI 1.09-1.13) and people with cancer ([OR] 4.21 95% CI 2.58-6.89) had a higher risk of dying from COVID-19 (p<0.05). Female sex was noted as a protective factor ([OR] 0.61 95% CI 0.40-0.92). Old age, male sex and cancer were independent prognostic factors for mortality. Three doses of SARS-CoV-2 vaccines and influenza vaccines were highly effective in preventing COVID-19-related deaths and hospital admissions. These findings suggest that flu vaccination can help control the pandemic.