The COVID-19 resource centre, hosted by Elsevier, provides free information in English and Mandarin on the novel coronavirus. Elsevier grants permission to make all its COVID-19-related research available in PubMed Central and other public repositories, allowing unrestricted reuse and analysis with acknowledgment of the original source. A nationwide, population-based seroepidemiological study in Spain estimated the prevalence of SARS-CoV-2 infection at 5.0% (95% CI 4.7–5.4) by a point-of-care test and 4.6% (4.3–5.0) by an immunoassay. Seroprevalence varied geographically, with higher rates around Madrid and lower rates in coastal areas. The study found that around a third of seropositive individuals were asymptomatic, and most PCR-confirmed cases had detectable antibodies. These findings highlight the need to maintain public health measures to prevent a new epidemic wave.The COVID-19 resource centre, hosted by Elsevier, provides free information in English and Mandarin on the novel coronavirus. Elsevier grants permission to make all its COVID-19-related research available in PubMed Central and other public repositories, allowing unrestricted reuse and analysis with acknowledgment of the original source. A nationwide, population-based seroepidemiological study in Spain estimated the prevalence of SARS-CoV-2 infection at 5.0% (95% CI 4.7–5.4) by a point-of-care test and 4.6% (4.3–5.0) by an immunoassay. Seroprevalence varied geographically, with higher rates around Madrid and lower rates in coastal areas. The study found that around a third of seropositive individuals were asymptomatic, and most PCR-confirmed cases had detectable antibodies. These findings highlight the need to maintain public health measures to prevent a new epidemic wave.