Nationally representative SARS-CoV-2 antibody prevalence estimates after the first epidemic wave in Mexico

Abstract

Seroprevalence surveys provide estimates of the extent of SARS-CoV-2 infections in the population, regardless of disease severity and test availability. In Mexico in 2020, COVID-19 cases reached a maximum in July and December. We aimed to estimate the national and regional seroprevalence of SARS-CoV-2 antibodies across demographic and socioeconomic groups in Mexico after the first wave, from August to November 2020. We used nationally representative survey data including 9,640 blood samples. Seroprevalence was estimated by socioeconomic and demographic characteristics, adjusting by the sensitivity and specificity of the immunoassay test. The national seroprevalence of SARS-CoV-2 antibodies was 24.9% (95%CI 22.2, 26.7), being lower for adults 60 years and older. We found higher seroprevalence among urban and metropolitan areas, low socioeconomic status, low education and workers. Among seropositive people, 67.3% were asymptomatic. Social distancing, lockdown measures and vaccination programs need to consider that vulnerable groups are more exposed to the virus and unable to comply with lockdown measures.

Fig. 1

Seroprevalence of SARS-CoV-2 across nine regions  in Mexico.

Fig. 2. Flowchart of participants in the serologic subsample in Ensanut 2020.

The flowchart of participants in the National Health and Nutrition Survey (Ensanut 2020). From the 36,024 subjects selected at the household level, a subsample of 21,707 were randomly selected to participate in the serologic sample. From those some could not be contacted and others declined to participate. We collected 9,640 venous samples.