Trends in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Seroprevalence in Massachusetts Estimated from Newborn Screening Specimens

Abstract

Background: Estimating the cumulative incidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is essential for setting public health policies. We leveraged deidentified Massachusetts newborn screening specimens as an accessible, retrospective source of maternal antibodies for estimating statewide seroprevalence in a nontest-seeking population.

Methods: We analyzed 72 117 newborn specimens collected from November 2019 through December 2020, representing 337 towns and cities across Massachusetts. Seroprevalence was estimated for the Massachusetts population after correcting for imperfect test specificity and nonrepresentative sampling using Bayesian multilevel regression and poststratification.

Results: Statewide seroprevalence was estimated to be 0.03% (90% credible interval [CI], 0.00-0.11) in November 2019 and rose to 1.47% (90% CI: 1.00-2.13) by May 2020, following sustained SARS-CoV-2 transmission in the spring. Seroprevalence plateaued from May onward, reaching 2.15% (90% CI: 1.56-2.98) in December 2020. Seroprevalence varied substantially by community and was particularly associated with community percent non-Hispanic Black (β = .024; 90% CI: 0.004-0.044); i.e., a 10% increase in community percent non-Hispanic Black was associated with 27% higher odds of seropositivity. Seroprevalence estimates had good concordance with reported case counts and wastewater surveillance for most of 2020, prior to the resurgence of transmission in winter.

Conclusions: Cumulative incidence of SARS-CoV-2 protective antibody in Massachusetts was low as of December 2020, indicating that a substantial fraction of the population was still susceptible. Maternal seroprevalence data from newborn screening can inform longitudinal trends and identify cities and towns at highest risk, particularly in settings where widespread diagnostic testing is unavailable.

Keywords: SARS-CoV-2; newborn screening; seroprevalence.

Figure 1.

IgG results of 288 anonymized specimens obtained in March 2019 tested by each of the 3 laboratories across 4 plates. Blue dots (dark gray in grayscale) are residual newborn screening dried blood spot specimens, red dots (light gray in grayscale) are positive controls, and black dots are diluent controls. Abbreviation: IgG, immunoglobulin G.

Figure 2.

Statewide longitudinal seroprevalence trend from November 2019 to December 2020 estimated using the monthly multilevel regression and poststratification model adjusting for test specificity. The mean seroprevalence estimates are indicated by the blue dots (dark gray in grayscale) with the error bars depicting 90% credible intervals; pink dots (light gray in grayscale) represent unadjusted weekly seroprevalence estimates.

Figure 3.

Longitudinal seroprevalence trends in cities and towns from November 2019 to December 2020 estimated using the monthly multilevel regression and poststratification model adjusting for test specificity. The 8 cities and towns with the highest lower 90% credible interval in December 2020 and at least 20 heel stick samples collected are shown. The mean seroprevalence estimates are indicated by the blue dots (dark gray in grayscale) with the error bars depicting the 90% credible intervals; pink dots (light gray in grayscale) represent unadjusted monthly seroprevalence estimates.

Figure 4.

Comparison of multilevel regression and poststratification seroprevalence estimates with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) surveillance data from reported cases and wastewater testing. a, Statewide longitudinal seroprevalence trend estimated from newborn screening samples (vertical bars) overlaid with cumulative incidence from MAVEN epidemiological surveillance data (smoothed line). b, Seroprevalence trends for 6 cities and towns (blue) overlaid with MAVEN cumulative incidence (smoothed line). c, Seroprevalence trend for the northern MWRA region (vertical bar) vs cumulative RNA copies per milliliter from wastewater SARS-CoV-2 testing for the same region (smoothed line). In all subpanels, the blue error bars depict the 90% credible interval for seroprevalence, and seroprevalence data are shifted backward by 3 weeks to match the timing of surveillance data. Abbreviations: MAVEN, Massachusetts Virtual Epidemiologic Network; MWRA, Massachusetts Water Resource Authority; NBS, newborn screening.

Figure 5.

Comparison of percent non-Hispanic Black (left) and percent Hispanic or Latino (right) with estimated seroprevalence by community. Dots indicate mean of the posterior seroprevalence distribution, and shaded regions indicate 90% credible intervals. Communities with a lower 90% credible interval above 3% seropositivity are labeled.