Prevalence of Antibodies to COVID-19 Due to Infection or Vaccination in US Adults
Authors: Stout Robert L , Rigatti Steven J 
Published: September 2023

Objective.—Determine the seroprevalence of SARS-CoV-2 infection and vaccination in a population applying for life insurance.
Setting.—This is a cross-sectional study of 2584 US life insurance applicants, to determine the seroprevalence of antibodies to COVID-19. This convenience sample was selected on two consecutive days April 25-26, 2022.
Results.—For COVID-19, 97.3% are seropositive, and 63.9% have antibodies to nucleocapsid protein, a marker of prior infection. An additional, 33.7% have been vaccinated with no serologic evidence of infection.
Methodology.—Serum and urine samples from a nationwide group of insurance applicants for routine risk assessment were collected. The examination of applicants typically occurs, in their homes, their place of employment, or a clinic. The paramedic exam occurs 7-14 days after the insurance application. Before the exam, an office assistant calls the applicant and inquires if they have been in contact with a person with SARS-CoV-2, been ill within the last 2 weeks, felt sick, or recently had a fever. If the applicant answers yes, the exam is rescheduled.
Before sample collection, the applicant reads and signs a consent form to release medical information and testing. Next, the examiner records the applicant’s blood pressure, height, and weight. Then, a blood and a urine sample are collected and sent with the consent form to our laboratory via Federal Express.
On April 25-26, 2022, we tested 2584 convenience samples from adult insurance applicants for the presence of antibodies to nucleocapsid and spike proteins from SARS-CoV-2. As a standard practice, we reported the client-specified test profile results to our life insurance carriers. In contrast, the COVID-19 test results were only available to the authors.
Patient and Public Involvement.—There was no patient involvement in study design, reporting of results, or journal publication selection. There was patient consent to publish de-identified study results. No public involvement occurred in the creation or completion of the study. The authors thank the participants in this study for approving the use of their blood samples to further society’s understanding of the SARS-CoV-19 pandemic.
Ethics Review.—Western Institutional Review Board reviewed the study design and determined it to be exempt under the Common Rule and applicable guidance. Therefore, it is exempt under 45 CFR § 46.104(d)(4) from using de-identified study samples for epidemiologic investigation, WIRB Work Order #1-1324846-1. In addition, all test subjects had signed a consent allowing research of their blood and urine samples with the removal of personally identifiable information.
Results.—The combined seroprevalence for antibodies to nucleocapsid, a marker of prior infection, and antibodies to spike protein, an indicator of either previous infection or vaccination, was 97.3%. Higher infection rates occur in younger vs older age groups, with a non-statistical difference for vaccinated and acquired natural immunity. For the age group 16-84, the total estimated seroprevalence of COVID-19 in the US is 249 million cases.
Conclusions.—The US population has widespread immune resistance to current variants of COVID-19 due to prior infection or vaccination. The infectivity of new variants and silent disease, independent of previous infection or vaccination, are the driving force behind the sporadic increase in clinical SARS-CoV-2 cases.