Persistence and Protective Potential of SARS-CoV-2 Antibody Levels After COVID-19 Vaccination in a West Virginia Nursing Home Cohort

Key Points Question What are the persistence and protective potential of SARS-CoV-2 antibody levels after vaccination in West Virginia nursing home residents and staff? Findings In this cross-sectional study of 2139 participants from West Virginia nursing home facilities, antibody levels decreased with time after vaccination but were restored with booster doses. During the Delta surge, individuals experiencing breakthrough infection had significantly lower antibody levels, but no significant association was found between antibody level and infection observed during the Omicron surge. Meaning Although these findings support the recommendation of booster doses to augment waning antibody responses, data are not conclusive in providing an antibody correlate of protection against infection.


Introduction
West Virginia prioritized COVID-19 vaccine delivery to nursing home residents because of reported higher rates of infection, severe illness, and death among older persons in chronic care facilities. 1,2In addition, nursing home staff were also prioritized for vaccination given their proximity to nursing home residents.As the COVID-19 pandemic unfolded, nursing home facilities have faced intense challenges combating outbreaks by implementing stringent safety protocols and offering increased testing and monitoring of nursing facility residents and staff.
The presence of antibodies (IgG) specific to the SARS-CoV-2 spike receptor binding domain (RBD) reflect previous vaccination or infection, whereas the presence of antibodies to nucleocapsid (N) protein reflect prior infection with SARS-CoV-2. 3 The persistence of humoral immunity (as reflected by circulating antibody concentrations) after SARS-CoV-2 vaccination is still being characterized; however, studies 4,5 suggest that anti-SARS-CoV-2 antibody levels may be lower in vaccinated patients residing in nursing homes and wane more rapidly.Because levels of spike IgG have been correlated with neutralizing antibody and accepted as a protective correlate for SARS-CoV-2 severe disease, recommendations for a third messenger RNA (mRNA) vaccination have been made, and a fourth vaccination was authorized for persons 50 years or older and others who are immunocompromised. 6,7In this study, we assessed SARS-CoV-2 spike antibody levels and their association with subsequent infection among West Virginia nursing home residents and staff who had previously received SARS-CoV-2 vaccination.

Study Design and Data Collection
Residents and staff from participating West Virginia nursing facilities who were 18 years or older and fully vaccinated with at least 2 doses of BNT162b2 (Pfizer) or mRNA-1273 (Moderna) or at least 1 dose of Ad26.COV2.S (Janssen/Johnson & Johnson) were eligible to participate in this cross-sectional study.Study involvement was voluntary, and data collection was limited to participating individuals.
The exclusion criteria included the presence of fatally rapid disease likely to result in death within less than 6 months.Nursing home staff, residents, and residents' families (if deemed appropriate by nursing home staff) were provided an information sheet explaining the study.A Health Insurance Portability and Accountability Act waiver of consent was approved by the West Virginia University Institutional Review Board.Data obtained were identifiable to the research team.Data were deidentified for the purposes of analysis.This study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.
A single serum specimen was collected from each participant between September 13 and November 30, 2021.At the time of sample collection, participants and/or nursing home staff provided the following information on participating individuals: name, date of birth, sex, race, nursing resident or staff, vaccine manufacturer and administration dates, and date of the last known (2) having exact first name, last name, and year and month of birth; or (3) having exact first name, last name, and year and day of birth.We also concluded 2 records to be a match when the only difference between records was using an abbreviated first name instead of a full name, using a similar first or last name with 1 or 2 extra letters, or using a similar first or last name with 1 or 2 different letters.
In the context of this article, fully vaccinated refers to participants who completed initial vaccination series (2 doses of the BNT162b2 or mRNA-1273 vaccine or 1 dose of the Ad26.COV2.S vaccine).Vaccine breakthrough infections are SARS-CoV-2 infections that occur at least 14 days after full vaccination.Boosted is defined as participants who received a third dose of the BNT162b2 or mRNA-1273 vaccine.

Serologic Assays
Serum was screened for anti-RBD and antinucleocapsid IgG with enzyme-linked immunosorbent assay (ELISA) using a modified protocol from Horspool et al. 8 Briefly, a 1:125 dilution of sample was applied in duplicate to plates coated with recombinant RBD (2 μg/μL) or N (1 μg/μL) antigen followed by a 5-minute incubation.All incubations were performed at 30 °C with gentle shaking (1.5 Hz).After plate washing, secondary antibody buffer (1:1000 dilution of goat antihuman IgG secondary antibody [Invitrogen], horseradish peroxidase in 3% milk diluted in 1% phosphate-buffered saline, and 0.5% Tween-20) was applied to the wells, followed by a 9-minute incubation.After final plate wash, 3,3′,5,5′-tetramethylbenzidine-stabilized substrate for horseradish peroxidase (Promega) was aliquoted to wells and incubated for 3 minutes.The reaction was stopped using 3 mol/L hydrochloride.Absorbance was read at 450 nm using a Sunrise spectrophotometer (Tecan), and the index was calculated by dividing the sample signal by the mean calibrator signal.Calibrator material consisted of a 1:16 000 dilution of convalescent plasma.The World Health Organization (WHO) international reference panel for anti-SARS-CoV-2 immunoglobulin panel was obtained from the National Institute for Biological Standards and Control (NIBSC) (code 20/268), and the mean index of panel samples was calculated for comparison purposes.
Measurement of neutralizing antibody was assessed in a subset of 95 participants to evaluate correlation with anti-RBD IgG indexes; specimens were selected to account for the entire ELISA reportable range.Angiotensin-converting enzyme 2-binding inhibition assay (SARS-CoV-2 Panel 13 V-PLEX neutralization kit; Meso Scale Diagnostics) was performed according to the manufacturer's instructions using a 1:10 dilution of participant serum.Electrochemiluminescence signal was obtained on a plate reader (QuickPlex SQ120 plate reader; Meso Scale Diagnostics).Data were analyzed by graphing linear regression of log electrochemiluminescence signal against corresponding IgG data obtained using ELISA.

Statistical Analysis
Frequency distributions of various study sample characteristics were generated.Abbreviations: NA, not available; RBD, receptor binding domain.
a A breakdown of race between nursing home residents and staff was not available for those whose race was reported as American Indian, Asian, Black, and Native Hawaiian.
b Other indicates participants who chose not to disclose their racial or ethnic status.
c Fully vaccinated is defined as receiving 2 doses of the BNT162b2 or mRNA-1273 or 1 dose of the Ad26.COV2.S vaccine.
d Boosted is defined as receiving an additional (third) dose of BNT162b2 or mRNA-1273 vaccine.
e Classifications were defined by internal validation testing.P < .001)(Table ).A total of 308 participants (14%) (183 residents and 125 staff) with no reported history of infection at the time of specimen collection yielded anti-N indexes of 1.7 or higher, likely indicative of unknown or undocumented past infection.

Assessment of Anti-RBD IgG Antibody Levels as a Correlate of Protection
Among the 95 participants identified with SARS-CoV-2 infection after specimen collection, 78 individuals had no record of a booster vaccine receipt after sample procurement.Among those 78 individuals (median [range] time after blood draw until infection: 71 [1-119] days), the median antibody index (calculated by dividing the sample signal by the mean calibrator signal) was 4.1 (95% CI, 2.9-6.8)compared with 5.8 (95% CI, 5.6-6.2) for individuals with no reported infection (P = .44).
Figure 3 shows distribution of anti-RBD IgG index levels in participants with defined exposures (ie, vaccination or breakthrough infection).Data were analyzed from participants with exposures reported within 14 to 77 days before specimen collection.Fully vaccinated participants with no history of SARS-CoV-2 infection had significantly lower antibody indexes (median, 8.0; 95% CI, 817 BAU/mL).
As of January 2022, 1 COVID-19-related death was reported within the cohort.This participant was a 76-year-old nursing home resident who was infected with SARS-CoV-2 at the time of specimen collection and died 9 days after serum collection.Anti-RBD and anti-N IgG indexes were negative (indexes were 0.5 for both tests) for this individual who had completed a 2-dose vaccination series approximately 7 months before specimen collection.

Discussion
This cross-sectional study of SARS-CoV-2 antibody levels among nursing home residents and staff demonstrates anti-RBD IgG antibody levels decreased with time after vaccination or infection, consistent with other reports 9,10 and supports recommendations for booster doses to augment immune responses.Fully vaccinated, nonboosted individuals who had previously vaccine breakthrough infections had significantly higher antibody levels compared with boosted  Data were from time-comparable cases with the most recent defined exposures (ie, vaccination or breakthrough infection) that occurred within 14 to 77 days before specimen collection.Individuals with breakthrough infections were fully vaccinated but not boosted.Orange line represents the median index.
a Significantly lower median antibody index compared with all other groups (all, P < .001).
b Significantly lower median antibody index compared with boosted individuals with previous infection (P < .001).

Findings
In this cross-sectional study of 2139 participants from West Virginia nursing home facilities, antibody levels decreased with time after vaccination but were restored with booster doses.During the Delta surge, individuals experiencing breakthrough infection had significantly lower antibody levels, but no significant association was found between antibody level and infection observed during the Omicron surge.Meaning Although these findings support the recommendation of booster doses to augment waning antibody responses, data are not conclusive in providing an antibody correlate of protection against infection.

Figure 2 .
Figure 2. Comparison of Anti-Receptor Binding Domain (RBD) IgG Index Levels in Participants With Documented SARS-CoV-2 Infection Occurring After Sample Procurement and Those With No Evidence of Subsequent Infection Delta-era infections A

Figure 3 .
Figure 3. Distribution of Anti-Receptor Binding Domain (RBD) IgG Index Levels Among Various Participant Groups 25

JAMA Network Open | Infectious Diseases
COVID-19 infection.Specimens were collected as a 1-time blood draw in serum separator tubes with

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Multivariate analysis was performed to evaluate the association between antibody indexes and independent variables, including time since vaccination, age, booster status, sex, and vaccine type.Antibody levels from participants who became infected after specimen collection were compared with those without infection to correlate antibody levels with subsequent infection.The linear model assessment was performed according to Akaike information criterion and statistical significance.A 2-sided P < .05impliesstatistical significance in this study.Statistical calculations were performed using Prism-GraphPad software, version 9 (GraphPad Inc).Forty-one of West Virginia's 95 nursing homes agreed to participate in the study.Reasons for nursing home nonparticipation included staffing issues, ongoing SARS-COV-2 institutional outbreaks that precluded external visitors, and inability of the hired phlebotomy organization to service the nursing home.Among those 41 nursing homes, there were 3109 residents and 2492 staff.The participating study population (ie, those who agreed to participate and met the inclusion criteria) included 2164 COVID-19 vaccinated participants, of whom 25 failed to provide sufficient samples for serologic testing and were excluded from the study.Among the 2139 participants included in the study 2he Wilcoxon rank sum test was used to assess the difference of continuous variables between subpopulations, whereas the Fisher exact test (or χ2test in the case of vaccine type comparison) was used for JAMA Network Open | Infectious Diseases Persistence and Protective Potential of SARS-CoV-2 Antibody Levels After COVID-19 Vaccination JAMA Network Open.2022;5(9):e2231334.doi:10.1001/jamanetworkopen.2022.31334(Reprinted)September13,2022 3/10 Downloaded From: https://jamanetwork.com/ on 09/23/2023 categorical variables.(median[range]age,67 [18-103] years; 1660 [78%] female; 2045 [96%] White, 44 [2%] Black, 7 [<1%] Asian, 1 [<1%] American Indian, 3 [<1%] native Hawaiian, and 39 participants [2%] who chose not to disclose their racial or ethnic status), 1086 were nursing home residents and 1053 were nursing home staff members (Table).Compared with staff, the nursing home residents were older, more likely to be men, and more likely to have received a vaccine booster dose (335 [31%] compared with 210 [20%]; P < .001).At the time of specimen collection, a higher percentage of nursing home residents reported previous SARS-CoV-2 infections compared with staff (372 [34%] compared with 236 [22%]; P < .001)(Table).Most of these individuals reported infections that occurred before full vaccination status 478 [79%]) and between November 2020 and January 2021 (382 [63%]).Prior vaccine breakthrough infections were reported by 128 participants (6%) (71 residents [6%] and 57 staff [5%]) at sample receipt, of which 105 infections (82%) occurred between August and October 2021 during the SARS-CoV-2 Delta surge in West Virginia (data on file, West Virginia University).As stated in the Methods section, vaccine breakthrough infections were monitored after specimen collection using the WVDHHR COVID-19 surveillance system.On the basis of available data, a total of 219 participants (10%) within this cohort experienced vaccine breakthrough infections between January 22, 2021, and January 16, 2022, with 197 (90%) of these participants having documented infections between August 2021and January 2022 during Delta and Omicron SARS-CoV-2 surges in West Virginia (Figure1).