Third wave of COVID-19 in Madrid, Spain.

A third wave of COVID-19 occurred after Christmas in Madrid, one of the European epicenters. We noticed six major differential features. First, household contacts were a large proportion of cases. Second, access to rapid antigen tests allowed prompt diagnosis and isolation. Third, clinically severe cases and mortality rates were lower than in prior waves. Fourth, the more transmissible B.1.1.7 strain was increasingly found. Fifth, vaccination benefits were seen in health care workers and nursing homes. Lastly, re-infections were more common. Before Easter, roughly 25% of the population in Madrid had been infected with SARS-CoV-2. Therefore, massive and accelerated vaccination campaigns are warranted to prevent new COVID-19 waves.