Trends in SARS-CoV-2 seroprevalence in Massachusetts

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Newborn screening (NBS) was first used to measure the seroprevalence of human immunodeficiency virus (HIV) in the late 1980s. This method is useful in monitoring SARS-CoV-2 infection in the absence of symptoms.

Study: Trends in the seroprevalence of SARS-CoV-2 in Massachusetts estimated from newborn screening samples. Image Credit: Simfalex / Shutterstock

Monitoring new disease outbreaks remains a challenge for disease surveillance networks. NBS programs serve as a source for such information. NBS programs collect dried blood spot samples for infants in central clinical laboratories where they are tested for signs of treatable genetic disorders. These infant blood samples contain maternal immunoglobulin (Ig) G antibodies that cross the placenta; Hence, they reflect the mother’s exposure to infectious agents.

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A new study was published in medRxiv Prep* The server reported the results, addressing questions about the incidence and prevalence of SARS-CoV-2 infection, from a retrospective, de-identified and systematic survey of SARS-CoV-2 seroprevalence among reproductive women in Massachusetts.

The study used data generated from newborn screening (NBS) samples. Women whose dried blood spot (DBS) samples for infants completed routine newborn screening were included. The DBS samples that arrived at the NBS screening program in March 2019 were the controls and the DBS from November 4, 2019, through December 31, 2020, were the study samples.

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In this study, SARS-CoV-2-reactive human (Ig)G-reactive monoclonal antibodies were prepared from the CR3022 variant gene expressed from plasmids. The receptor-binding domain (RBD) of the spike protein was expressed using HEK-293F cells and prepared.


IgG antibody specific to RBD protein was detected in residues of DBSs in the Massachusetts NBS program by adapting a previously described enzyme-linked immunosorbent assay (ELISA) designed for serum.

The seropositivity rates of the unidentified neonatal DBS cohort were measured in a subset of the remaining DBS – from a period believed to be significantly predating the outbreak of COVID-19. The lower positive controls depicted IgG concentrations significantly higher than the average of the tested samples and all above the values ​​of the tested samples.

There were 1,817 putative serotypes from March 2019, of which seven (0.39%) were seropositive for SARS-CoV-2. While among the 72,117 study samples, 1,261 (1.75% statewide) were seropositive and 45 individuals were seropositive from November and December 2019. As of November and December 2019, the mean inhibition was 1.45%, confirming that most The seropositive individuals from 2019 were false positive.

Meanwhile, the statewide monthly seroprevalence rate in early November 2019 was 0.03%, with a 90% confidence interval (CI) of 0.00-0.11% – remaining low until May 2020. After that, the seroprevalence increased to 1.47% After SARS persists. – The transmission of the emerging corona virus – COV-2 in the spring and stabilized at about 2% at the beginning of July 2020, reflecting the decrease in transmission in the summer months, due to the implementation of preventive measures. Meanwhile, the seroprevalence estimate for December 2020 was 2.15%.

Trends at the country level showed similar qualitative results. Total seropositivity varied widely across the state. However, cities with high seroprevalence showed qualitative trajectories similar to the general trends at the state level.

Whereas, presentations of reliable intervals also varied, reflecting uncertainty due to smaller sample sizes in some cities. For example – Boston seroprevalence estimate was 0.05% (90% CI [0.00, 0.17]) in November 2019, which had risen to 3.56% at the end of 2020 – slightly higher than in the state. In addition, modeling time has consistently yielded similar qualitative trends.

Good qualitative consistency was obtained by seroprevalence levels and cumulative incidence pathways for MAVEN from 2019-2020. However, there was a divergence between the curves at the end of 2020. This means that the seropositivity in the heel stick group did not rise as sharply as cases during the winter resurgence. The results showed a deviation between the DBS data and many other sources of SARS-CoV-2 monitoring at the end of the sampling timeline.

When examining community-wide factors associated with increased seropositivity, it was found that the incidence of seropositivity among non-Hispanic blacks and Hispanics or Hispanics increased in several cities and towns, including Brockton, Springfield, Everett, Chelsea, Lynn, and Lawrence. Therefore, it has been suggested that some additional sociodemographic variables require further study to characterize their association with seropositivity.


The current study provides a strategy to systematically assess and estimate the cumulative population-wide incidence of SARS-CoV-2 by evaluating the distribution of maternal antibodies at the state level and overtime. It has been stated that NBS can serve as a readily available data source and is most useful for informing estimates of cumulative incidence in areas where widespread infection testing is still unavailable or remains highly biased.

*Important note

medRxiv publishes preliminary scientific reports that are not subject to peer review, and therefore should not be considered conclusive, guide clinical practice/health-related behavior, or be treated as established information.


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