Between April 27 and May 11, 2020, seroprevalence for the entire country was 5·0% (95% CI 4·7–5·4) by the point-of-care test and 4·6% (4·3–5·0) by immunoassay

In seven provinces in the central part of Spain, including Madrid, seroprevalence was greater than 10% by both the point-of-care test and immunoassay separately.

In provinces along the coast, seroprevalence was greater than 5% only in Barcelona.

According to the point-of-care test, seroprevalence was 1·1% (95% CI 0·3–3·5) in infants younger than 1 year and 3·1% (2·2–4·2) in children aged 5–9 years, increasing with age until plateauing around 6% in people aged 45 years or older.

According to the immunoassay, seroprevalence was lower in the oldest age groups (≥85 years) compared with other adults.

Among those with a positive test, the proportion of individuals who reported anosmia or three or more symptoms compatible with COVID-19 was 49·1% (95% CI 46·2–51·9) for the point-of-care test and 54·2% (51·0–57·2) for the immunoassay.

The proportion of individuals with a positive test who were asymptomatic was 32·7% (30·2–35·4) and 28·5% (25·6–31·6), respectively,