This study aims to measure the impact of COVID-19 on Basque nursing homes in terms of resident mortality, and to identify nursing home factors associated with risk of death from COVID-19, as well as nursing-home profiles that have been most impacted by COVID-19.

The study will cover the period from March 2020 to June 2021 and will involve three different types of analysis:

• Estimation of excess mortality in the nursing home population and the general older population in the Basque Country. The aim of this part of the study will be to measure the “net” impact of COVID-19 on older people’s mortality, by measuring excess mortality and the fraction of that excess mortality that is directly attributable to COVID-19, and by comparing the nursing home population with community dwelling older adults. The analysis will also look into the temporal distribution of excess mortality in the nursing home population, to estimate de differential impact of the pandemic on the first and second waves, and the post-vaccination period.
• Analysis of nursing home level variance on overall and COVID-19 resident mortality, and identification of nursing home factors associated with resident deaths. Individual level data will be obtained from the Basque Health Service’s information system (Osakidetza) on SARS-CoV-2 infection and registered deaths, covering the whole nursing home population from March 2020 to June 2021. Multilevel logistic regression models will be applied to this data to estimate the proportion of individual variance on risk of mortality that lies at the nursing home level (as opposed to the individual level) and, therefore, determine how relevant nursing home characteristics or prevention measures can be in explaining risk of death for infected and non-infected service users. Depending on the significance of these general contextual effects, the association between specific nursing home characteristics such as size, ownership, staff-to-resident ratio or unitary cost and risk of mortality will be estimated.
• Typology of nursing homes in terms of mortality impact. Cluster analysis will be employed to identify characteristics of nursing home facilities that make them more vulnerable in terms of COVID-19 mortality. Factors significantly associated with mortality in the previous multilevel logistic regression models will be used to identify relevant nursing home clusters.

The main outputs of the study will be:

• Estimation of excess mortality in the Basque older population and the population living in nursing homes for the elderly in the period March 2020 to June 2021
• Estimation of the fraction of excess mortality that is directly attributable to COVID-19
• Estimation of individual level variability in overall and COVID-19 mortality that lies at the nursing home facility level.
• Estimation of the associations between nursing home characteristics and risk of mortality (size, ownership, resident-to-staff ratio, unitary cost, etc.)
• Typology of nursing homes and identification of clusters that are most vulnerable in terms of COVID-19 mortality.