The NHANES program suspended field operations in March 2020 due to the coronavirus disease 2019 (COVID-19) pandemic. As a result, data collection for the NHANES 2019-2020 cycle was not completed and the collected data are not nationally representative. Therefore, data collected from 2019 to March 2020 were combined with data from the NHANES 2017-2018 cycle to form a nationally representative sample of NHANES 2017-March 2020 pre-pandemic data. These data are available to the public. Please refer to the Analytic Notes section for more details on the use of the data.
Local poliovirus transmission has been eliminated from the United States since 1979 (Drutz et. al., 2000); however, transmission of wild poliovirus has never been interrupted in Pakistan or Afghanistan, and multiple countries continue to experience outbreaks caused by circulating vaccine-derived poliovirus (Geiger et. al., 2024). The continued global circulation of polioviruses poses a risk of imported cases in the United States. Furthermore, vaccination rates for poliovirus are declining among children in much of the United States (Seither et. al., 2024), leaving a higher percentage of the U.S. population susceptible to paralysis if infected with poliovirus. In 2022, the first domestically-acquired infection with poliovirus since 1979 was detected in the United States in an unvaccinated young adult residing in New York State who presented with paralytic polio and no history of recent travel (Link-Gelles et. al., 2022). Following the identification of this polio case, poliovirus was detected in wastewater samples in the case patient’s county and a neighboring county. This, combined with the fact that poliovirus vaccination was found to be much lower than the national average in the case patient’s county, led to heightened risk of outbreak in the region and a prolonged public health response, although no further cases were identified.
Data on poliovirus seroprevalence in the United States are limited (Wallace et. al., 2016; Wallace et. al., 2017). Analysis of NHANES sera from 2017–2020 will provide updated information on the seroprevalence of poliovirus in the United States to evaluate whether immunity in children and adults remains robust. Although undervaccinated communities exist in the United States, which poses a risk for poliovirus spread in the event of an imported poliovirus infection, ensuring sufficient national immunity to poliovirus infection and documenting trends in poliovirus immunity among age cohorts over time will provide valuable information for poliovirus prevention.
Examined participants aged 6-59 years were eligible.
Stored serum specimens were processed, stored, and shipped to the National Center for Immunization and Respiratory Diseases Laboratories, Centers for Disease Control and Prevention, Atlanta, GA for analysis.
The lab method for this component in the NHANES 2017–March 2020 cycle was different from the previous poliovirus serology file (e.g. SSPOLI_F).
A microneutralization assay was used to test for serotype-specific poliovirus antibodies (Weldon et. al., 2016). The 96-well polio microneutralization assay is a CLIA-approved test that has been used by the CDC laboratory in seroprevalence studies and human vaccine clinical trials. This assay uses 100 µl of sera to test levels of neutralizing antibodies to each of the three poliovirus types (Type 1, Type 2, and Type 3). Specimens tested using the microneutralization assay are stored at ≤-20°C and managed using the CDC-standard electronic laboratory information management system.
The CLIA-approved poliovirus microneutralization assay measures levels of serotype-specific neutralizing antibodies against all three poliovirus types. The technical basis of the test is that the presence of anti-poliovirus antibodies in a sample (e.g., serum) will bind the virus and block infection of susceptible cells. Poliovirus infection of susceptible cells is cytopathic, so virus that is not bound by neutralizing antibody can infect and kill target cells. Levels of poliovirus neutralizing antibodies are quantified by performing serial dilutions of samples and measuring the 50% endpoint titer or the last dilution of a sample that protects susceptible cells from poliovirus-induced cytopathic effects. The poliovirus strains tested were Sabin 1, Sabin 2, and Sabin 3.
Performance Characteristics of Qualitative Assays
Sensitivity is compared using the lowest concentration of an analyte that can be measured.
Specificity is measured using neutralizing antibodies present in sera from animals infected with a single poliovirus type or spiked human serum samples with neutralizing antibodies against a single poliovirus type. Sera from animals immunized with a related Enterovirus coxsackiepol virus is used as a negative control to assess assay specificity. Naïve animal sera and immunoglobulin depleted human sera are also used as negative controls.
Accuracy measures the level of agreement between the neutralization levels of samples within a test run. This is measured as a percent of coefficient of variation (%CV) using 50 human serum samples from healthy U.S. adults vaccinated for polio (seropositive samples) and an additional 7 human serum samples from healthy U.S. adults without documentation of polio vaccination (seronegative samples). The %CV is calculated as the standard deviation of neutralizing antibody titers for each poliovirus type over the mean neutralizing antibody mean titer for each poliovirus type × 100.
Reproducibility measures the ability of a method to yield similar neutralizing antibody titers for the same sample when tested over different testing runs. This is measured for 5 different testing runs and also expressed as %CV. Average CVs should not exceed 20% for each serotype.
The CLIA-approved poliovirus microneutralization assay has 100% sensitivity for all 3 poliovirus serotypes; 100% clinical specificity for each poliovirus serotype; analytical accuracy of 95% for serotypes 1 and 2 and 81% for serotype 3; and reproducibility with less than 8% coefficient of variation for all 3 serotypes. Every testing run must meet two quality controls: back titration levels for each virus used must fall within 2.0 +/- 0.5 log10 and reference sera must meet previously established type-specific ranges. Based on prior assay performance, 98% of testing runs result in a qualitative and quantitative result for all 3 poliovirus serotypes. Although not anticipated to be necessary, any repeat testing would require additional sample volume.
Data were received after all analyses were complete. The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.
Data for quantitative variables are included as reported by the testing laboratory:
SSPV1Q
Poliovirus serotype 1 quantitative (SSPV1Q) provides a quantitative titer result based on the number of 2-fold serial dilutions. For example, a value of 4 would mean a titer value of 4 log2 (i.e. 24 or 1:16 dilution).
SSPV2Q
Poliovirus serotype 2 quantitative (SSPV2Q) provides a quantitative titer result based on the number of 2-fold serial dilutions. For example, a value of 4 would mean a titer value of 4 log2 (i.e. 24 or 1:16 dilution).
SSPV3Q
Poliovirus serotype 3 quantitative (SSPV3Q) provides a quantitative titer result based on the number of 2-fold serial dilutions. For example, a value of 4 would mean a titer value of 4 log2 (i.e. 24 or 1:16 dilution).
Derived variables were created in this data file:
SSPV1I
Poliovirus serotype 1 interpretation (SSPV1I) was coded as 1 (positive) when Poliovirus serotype 1 quantitative titer value (SSPV1Q) was greater than or equal to 3 and coded as 2 (negative) when SSPV1Q was less than 3.
SSPV2I
Poliovirus serotype 2 interpretation (SSPV2I) was coded as 1 (positive) when Poliovirus serotype 2 quantitative titer value (SSPV2Q) was greater than or equal to 3 and coded as 2 (negative) when SSPV2Q was less than 3.
SSPV3I
Poliovirus serotype 3 interpretation (SSPV3I) was coded as 1 (positive) when Poliovirus serotype 3 quantitative titer value (SSPV3Q) was greater than or equal to 3 and coded as 2 (negative) when SSPV3Q was less than 3.
The COVID-19 pandemic required suspension of NHANES 2019-2020 field operations in March 2020 after data were collected in 18 of the 30 survey locations in the 2019-2020 sample. Data collection was cancelled for the remaining 12 locations. Because the collected data from 18 locations were not nationally representative, these data were combined with the previous cycle (2017-2018) to create a 2017-March 2020 pre-pandemic data file. A special weighting process was applied to the 2017-March 2020 pre-pandemic data file. The resulting sample weights in the present file should be used to calculate estimates from the combined cycles. These sample weights are not appropriate for independent analyses of the 2019-2020 data and will not yield nationally representative results for either the 2017-2018 data alone or the 2019-March 2020 data alone. Please refer to the NHANES website for additional information for the NHANES 2017-March 2020 pre-pandemic data.
Refer to the 2017-2018 and 2019-2020 Laboratory Data Overviews for general information on NHANES laboratory data.
There are over 800 laboratory tests performed on NHANES participants. However, not all participants provided biospecimens or enough volume for all the tests to be performed. Additionally, availability of specimens for surplus projects is lower than for other laboratory tests performed on NHANES participants. The specimen availability can also vary by age or other population characteristics. Analysts should evaluate the extent of missing data in the dataset related to the outcome of interest as well as any predictor variables used in the analyses to determine whether additional re-weighting for item non-response is necessary.
Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for details on the use of sample weights and analytic issues.
Subsample Weights
The analytes included in this dataset were measured in examined participants aged 6-59 years. Special sample weights are required to analyze these data properly. Specific sample weights for this subsample, WTSSMMPP, are included in this data file and should be used when analyzing these data. The sample weights created for this file used the examination sample weight, i.e., WTMECPRP, as the base weight. The base weight was adjusted for additional nonresponse to these lab tests and re-poststratified to the population total using sex, age, and race/Hispanic origin. Participants who were part of the eligible population, but who did not provide a serum specimen, or did not have sufficient volume of biospecimens, or who did not give consent for their specimens to be used for future research are included in the file, but they have a sample weight assigned “0” in their records.
Demographic and Other Related Variables
The analysis of NHANES laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2017-March 2020 Pre-Pandemic Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the sample design variables. The recommended procedure for variance estimation requires use of stratum and PSU variables (SDMVSTRA and SDMVPSU, respectively) in the demographic data file.
This laboratory data file can be linked to the other NHANES data files using the unique survey participant identifier (i.e., SEQN).
Detection Limits
The detection limits were constant for all of the analytes in the data set.
The assay provides a qualitative assessment for the presence of type-specific neutralizing antibodies (seropositive or seronegative) and a quantitative level of type-specific neutralizing antibodies ranging from 2.50-10.50 log2. Neutralizing antibody levels of less than 3.00 log2 are considered seronegative. No levels below the lower limit of detection (LLOD) or above the upper limit of detection (ULOD) are reported. The LLOD and ULOD, presented as the number of 2-fold serial dilutions, are:
| Variable Name | SAS Label | LLOD | ULOD |
| SSPV1Q | Poliovirus serotype 1 quantitative | 2.50 | 10.50 |
| SSPV2Q | Poliovirus serotype 2 quantitative | 2.50 | 10.50 |
| SSPV3Q | Poliovirus serotype 3 quantitative | 2.50 | 10.50 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 3203.163986 to 425710.13599 | Range of Values | 6738 | 6738 | |
| 0 | Participants 6-59 years with no lab specimen | 2319 | 9057 | |
| . | Missing | 0 | 9057 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 2.5 to 10.5 | Range of Values | 6707 | 6707 | |
| . | Missing | 2350 | 9057 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 1 | Positive | 5964 | 5964 | |
| 2 | Negative | 743 | 6707 | |
| . | Missing | 2350 | 9057 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 2.5 to 10.5 | Range of Values | 6707 | 6707 | |
| . | Missing | 2350 | 9057 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 1 | Positive | 6217 | 6217 | |
| 2 | Negative | 490 | 6707 | |
| . | Missing | 2350 | 9057 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 2.5 to 10.5 | Range of Values | 6707 | 6707 | |
| . | Missing | 2350 | 9057 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 1 | Positive | 5419 | 5419 | |
| 2 | Negative | 1288 | 6707 | |
| . | Missing | 2350 | 9057 |