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.

SARS-CoV-2 infection fatality rate after the first epidemic wave in Mexico

“…Considering the challenges to generalizability conferred by the 51% participation rate, in a previous study, we conducted a sensitivity analysis of the magnitude of possible selection bias in ENSANUT 2020 Covid-19. 8 After adjustment, the national seroprevalence changed from 24.9% (95% CI 22.2, 26.7) to 23.8% (95% CI 21.3, 25.4). More information on this adjustment can be found elsewhere.…”

“…To estimate the total number of people infected with SARS-CoV-2 in Mexico between the onset of the pandemic and late 2020, we obtained seroprevalence data from ENSANUT 2020 Covid-19—a survey that is representative at the national and regional levels (nine regions), and is also representative for both urban and rural areas. 7 , 8 Briefly, fieldwork teams visited households and randomly selected one person from each of six potential age groups (1–4, 5–9, 10–19, 20–34, 35–49 and ≥50 years) to provide a blood sample. A total of 9640 serum samples (51% participation rate) for SARS-CoV-2 antibody determination were obtained between August and November 2020 ( Supplementary Table S1 , available as Supplementary data at IJE online, presents all regions surveyed and collection dates).…”

“…Seroprevalence (N-protein) was corrected by an internal validation study, which established that Roche’s Elecsys assay had a 92.02% sensitivity (95% CI 88.57, 94.5) and a 99.52% specificity (95% CI 97.35, 99.92). 8 Estimates of seroprevalence were calculated using sampling weights, whereas the absolute number of people with evidence of recent or prior infection was estimated by multiplying the age- and sex-specific adjusted seroprevalence by the total size of the corresponding population group, according to the 2020 census. 9 The same procedure was used to calculate the number of seropositive people by region and urbanization strata.…”

“…More information on this adjustment can be found elsewhere. 8 Because the 95% CIs overlapped, 8 we used the original estimate in this paper, without adjusting.…”

Comparing the evolutionary dynamics of predominant SARS-CoV-2 virus lineages co-circulating in Mexico

“…In Mexico, a vaccination rate of > 50% (re ecting the proportion of the population immunized with at least two doses) was only reached after December 2021 29,75 , suggesting that immunity levels in the population depended mostly on virus pre-exposure levels. By December 2020, a nationwide representative seroprevalence was estimated to be of ~ 33.5% 76,77 .…”