AI = accumulated incidence = cases per 100,000 inhabitants. PCR+ = positive COVID-19 diagnosis by PCR or antigen. PCR+ 14 days = positive COVID-19 diagnoses by PCR or antigen over last 14 days. Spain's four-tier systems classifies regions from low-extreme risk as follows: BAJO AI between 25-50; MEDIO AI between 50-150; ALO AI between 150-250; EXTREMO AI above 250.