In a recent study published on the medRxiv* preprint server, researchers at East Carolina University reported the depletion of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seropositivity in healthy young adults over a seven-month period.
Study: Loss of SARS-CoV-2 Seropositivity among Healthy Young Adults over Seven Months. Image Credit: Prostock-studio / Shutterstock.com
Most higher education institutions have offered SARS-CoV-2 testing to symptomatic students, as well as those with recent contacts of suspected or confirmed coronavirus disease 2019 (COVID-19) as young adults returned to campus in the fall of 2020 in the United States.
Young adults can still transmit SARS-CoV-2 while asymptomatic. Thus, screening asymptomatic individuals in a group environment has been a crucial aspect of a comprehensive plan to limit viral transmission.
Long-term studies on COVID-19 patients, long-term care residents, and healthcare staff have described the longevity of immunoglobulin G (IgG) antibodies targeting SARS-CoV-2. According to available reports, people with asymptomatic to mild COVID-19 have reduced peak antibody titers, with those who have recovered from SARS-CoV-2 infection exhibiting a rapid decline in IgG titers.
However, longitudinal data regarding SARS-CoV-2 seroprevalence conversion and reversion in healthy young adults studying in a university setting are scarce. Furthermore, the durability of immunity in healthy young adults after recovering from COVID-19 is not well understood.
About the study
In the current study, researchers performed a longitudinal analysis to evaluate immunity established by SARS-CoV-2 infection in university students over a seven-month period. They hypothesized that IgG levels deteriorate over time, which is congruent to evidence obtained from previous studies conducted among medical professionals.
Antibodies targeting the SARS-CoV-2 spike (S) and nucleocapsid (N) antigens were quantified and referred to as S-IgG and N-IgG, respectively.
In a cohort of university students, scientists explored N-IgG seroprevalence, the time required for N-IgG establishment, and the incidence of N-IgG seroreversion for seven months. This data was contrasted with S-IgG development.
All study participants were enrolled at a public university and lived in Pitt County, North Carolina. Any undergraduate or graduate student aged 18 years or older who provided a Pitt County residential address, was enrolled full-time or part-time in the fall semester of 2020 and spoke English was eligible to participate in the study.
Between August 26, 2020, and October 28, 2020, university students participated in the study once a week for ten weeks. By November 17, 2020, 136 young adults had finished at least one study visit.
Between August 26, 2020, and March 31, 2021, all study participants provided nasal swabs and blood samples and completed an online survey at two-week intervals.
A total of 55 self-selected and 81 randomly selected eligible students completed at least one clinic visit during the initial SARS-CoV-2 wave. Taken together, 63.2% of the 136 students in wave 1 completed all planned research visits, while 71.3% from the first wave reconsented for the second wave.
Between August 26, 2020, and March 31, 2021, 12 students completed all scheduled research visits. Thirteen study visits were reported in the first wave, while only three were reported in the second wave.
The frequency of a positive result for N-IgG was 9.78% among 695 serum samples examined during the follow-up period. About 68% of individuals in a cohort of 22 young adults monitored for seven months exhibited a decline in SARS-CoV-2 N-IgG positivity below the threshold during the 140-day period.
Descriptive Statistics of nucleocapsid (N) IgG among young adults by collection date
Subjects who were recently vaccinated against COVID-19 had significantly heightened S-IgG levels beginning in January 2021. Although S-IgG remained detectable in these vaccinated students, these levels began to decline between February and March 2021. Thus, anti-S-IgG exhibits significant persistence relative to anti-N-IgG.
The current findings were comparable with prior research among non-hospitalized patients, as detectable N-IgG was absent in 65% of participants during the study period.
According to the study findings, young adults with mild or asymptomatic COVID-19 exhibit a faster peak and much faster decline in their peak N-IgG antibody responses as compared to hospitalized patients. Furthermore, repeated measurements of serum SARS-CoV-2 antibody levels in a young adult university cohort provide information regarding adaptive immunity through antibody retention and depletion.
Overall, the study findings indicate that SARS-CoV-2 N-IgG levels in healthy young adults decline to an undetectable threshold in five months. Comparatively, S-IgG remains consistently high for several months following infection and rose considerably after vaccination.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.