A recent mBio study aimed to ascertain the durability and effectiveness of immune responses against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in terms of spike-binding antibody titers.

Study: SARS-CoV-2 Spike-Binding Antibody Longevity and Protection from Reinfection with Antigenically Similar SARS-CoV-2 Variants. Image Credit: ustas7777777 / Shutterstock.com

Background

SARS-CoV-2 infection, which causes the coronavirus disease 2019 (COVID-19), has infected over 605 million and caused over 6.4 million deaths since first emerging at the end of 2019. Due to repeated occupational exposures, healthcare workers (HCWs) are particularly vulnerable to COVID-19. 

On February 29, 2020, the Mount Sinai Health System in New York City detected the first SARS-CoV-2 infection in the state. Due to the large number of patients with severe COVID-19, this initial outbreak quickly overwhelmed local health care systems.

About the study

In April 2020, HCWs from the Mount Sinai Health System, with and without documented COVID-19, enrolled in the Protection Associated with Rapid Immunity to SARS-CoV-2 (PARIS) cohort.

Overall, 501 individuals registered for the PARIS trial between April 2020 and August 2021, 400 of whom were included in the final analysis. Whereas 150 study participants had a history of COVID-19, the remaining 250 did not. The median age of the participants was 35 years, with 68% female. 

A sensitive and specific quantitative enzyme-linked immunosorbent assay (ELISA) was used to measure full-length spike-binding immunoglobulin G (IgG) antibody titers in the serum every two to four weeks. At the same time intervals, information regarding possible exposures and clinical symptoms suggestive of SARS-CoV-2 infection was collected.

A subset of 137 study participants with known dates of COVID-19 diagnosis was used to obtain a total of 813 unique spike-binding measurements. In addition, demographic variables like sex and age were examined for possible associations with spike antibody durability. 

The association between spike-binding IgG and protection against reinfection with genetically similar SARS-CoV-2 variants was also investigated. From July 2020 and August 2021, 11 new SARS-CoV-2 infections were identified among PARIS participants.

Study findings

Among the subset of 137 study participants with a history of COVID-19, spike-binding IgG titers varied greatly from 1:80 to 1:6,400. Notably, over 59% of study participants exhibited antibody titers at or above 1:800 at their initial visit.

These antibody titers decreased over the first three months; however, they subsequently stabilized for up to one year after recovering from COVID-19. Notably, this decay in antibody levels was more significant in those with higher antibody levels.

Only 6% of COVID-19 survivors who initially exhibited positive IgG levels tested negative throughout the follow-up period. Importantly, each of these individuals had initially low antibody levels, thus indicating the relatively rare risk of seroreversion in these situations.

Older participants over the age of 40 had 1.62-fold higher antibody titers as compared to younger participants. Antibody titers in female participants were also about 1.4-fold higher as compared to those of male participants.

Ten of the 11 individuals who were reinfected with SARS-CoV-2 had been reinfected when ancestral SARS-CoV-2 strains were in circulation. This finding indicates that spike-binding IgG antibodies elicited by the ancestral SARS-CoV-2 strain provided robust protection against reinfection.

Limitations

It is worth noting that the molecular tests used in this study could not be conducted for a significant number of the participants at the time of infection; therefore, the date of disease onset was based on retrospective reports of clinical signs and symptoms. Thus, recall bias is likely in reported illness onsets.

The relatively homogenous exposures of HCWs were assumed to have only a minor impact on the conclusions. 

Secondly, the researchers were unable to effectively assess how circulating SARS-CoV-2 variants of concern (VOCs) may affect one's risk of reinfection following natural infection.

Written by

Nidhi Saha

I am a medical content writer and editor. My interests lie in public health awareness and medical communication. I have worked as a clinical dentist and as a consultant research writer in an Indian medical publishing house. It is my constant endeavor is to update knowledge on newer treatment modalities relating to various medical fields. I have also aided in proofreading and publication of manuscripts in accredited medical journals. I like to sketch, read and listen to music in my leisure time.