SARS-CoV-2 Serology and Self-Reported Infection Among Adults - National Health and Nutrition Examination Survey, United States, August 2021-May 2022

Abstract

CDC COVID-19 surveillance systems monitor SARS-CoV-2 antibody prevalence to collect information about asymptomatic, undiagnosed, and unreported disease using national convenience samples of blood donor data from commercial laboratories (1,2). However, nonrandom sampling of data from these systems could affect prevalence estimates (1-3). The National Health and Nutrition Examination Survey (NHANES) collects SARS-CoV-2 serology data among a sample of the general U.S. civilian population (4). In addition, NHANES collects self-reported COVID-19 vaccination and disease history, and its statistical sampling design is not based on health care access or blood donation. Therefore, NHANES data can be used to better quantify asymptomatic SARS-CoV-2 infection prevalence and seropositivity attained through infection without vaccination. Preliminary NHANES 2021-2022 results indicated that 41.6% of adults aged ≥18 years had serology indicative of past infection and that 43.7% of these adults, including 57.1% of non-Hispanic Black or African American (Black) adults, reported never having had COVID-19, possibly representing asymptomatic infection. In addition, 25.5% of adults whose serology indicated past infection reported never having received COVID-19 vaccination. Prevalences of seropositivity in the absence of vaccination were higher among younger adults and Black adults, reflecting the lower observed vaccination rates among these groups (5). These findings raise health equity concerns given the disparities observed in SARS-CoV-2 infection and COVID-19 vaccination. Results from NHANES 2021-2022 can guide ongoing efforts to achieve vaccine equity in COVID-19 primary vaccination series and booster dose coverage.

FIGURE 1

Combined SARS-CoV-2 anti-spike and anti-nucleocapsid antibody testing results among adults aged ≥18 years who were infected and possibly vaccinated (A) and those vaccinated without infection (B), by age group, sex, race and Hispanic origin, and education — National Health and Nutrition Examination Survey, United States, August 2021–May 2022 Abbreviations: anti-N = anti-nucleocapsid; anti-S = anti-spike. * Positivity for SARS-CoV-2 anti-S antibodies (previous infection, vaccination, or both). ^† Positivity for SARS-CoV-2 anti-N antibodies (previous infection). ^§ The category “other, non-Hispanic” includes non-Hispanic participants who reported being either American Indian or Alaska Native, Asian, Native Hawaiian or other Pacific Islander, or multiple race. ^¶ Preliminary sample = 1,574, unweighted data; information on education was missing for 63 adults.

FIGURE 2

Percentage of adults aged ≥18 years with both SARS-CoV-2 anti-spike and anti-nucleocapsid antibodies who reported never having had COVID-19 (A) or never having received any COVID-19 vaccine (B), by age group, sex, race and Hispanic origin, and education — National Health and Nutrition Examination Survey, United States, August 2021–May 2022 * Positivity for SARS-CoV-2 anti-spike antibodies (previous infection, vaccination, or both). ^† Positivity for SARS-CoV-2 anti- nucleocapsid antibodies (previous infection). ^§ Negative response to the question, “Have you ever had COVID-19, or the illness caused by the Coronavirus Disease 2019?” ^¶ Responded “zero doses” to the question, “How many doses of COVID-19 vaccine have you received? Please include booster shots and any additional doses.” ** The category “other, non-Hispanic” includes non-Hispanic participants who reported being either American Indian or Alaska Native, Asian, Native Hawaiian or other Pacific Islander, or multiple race. ^†† Preliminary sample = 655, unweighted data; information on education was missing for 36 adults.