key: cord-0916632-kr3rlvuf
authors: Ruopp, Marcus D.; Strymish, Judy; Dryjowicz-Burek, Jonathan; Creedon, Katie; Gupta, Kalpana
title: Durability of SARS-CoV-2 IgG Antibody Among Residents in a Long-Term Care Community
date: 2021-01-23
journal: J Am Med Dir Assoc
DOI: 10.1016/j.jamda.2021.01.066
sha: b8f054e22d77aeec6836235718f1c3dd278e4982
doc_id: 916632
cord_uid: kr3rlvuf

nan

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of 2 coronavirus disease 2019 (COVID-19), has spread rapidly around the world since first identified 3 in Wuhan, China, in December 2019. 1 Long-term care residents have been among the hardest 4 impacted by COVID-19. Over 500,000 residents in nursing homes and long-term care facilities 5 have been infected in the United States, accounting for 40% of the total deaths from Covid-19. 2 6 Among survivors, an understanding of the expected durability of the antibody response may be 7 helpful in estimating the risk of a new infection. This is particularly important in preparation for 8 another surge. Previous studies have reported durability of response up to four months in adults 9

with an average age under sixty. 3-5 However, little is known about the durability of antibody 10 response in older, potentially less immunogenic long-term care populations. 6,7 We assessed the 11 durability of antibody response in our long-term care population from the time of initial infection 12 over a six month period. 13

The VA Boston Healthcare System includes a 112-bed skilled nursing facility for veterans 15 needing long-term care. All residents had nasal SARS-CoV-2 PCR testing performed at baseline 16 when all were asymptomatic and negative, and then again for symptoms and for surveillance at 17 repeated intervals. Serum antibody testing was also performed after the first surge and then again 18 periodically over the following six months as part of routine surveillance. 19

The SARS-CoV-2 IgG assay was performed on the Abbott Architect i2000SR (Abbott 20 Diagnostics, Chicago, USA). This assay is a chemiluminescent immunoassay which detects IgG 21 against the nucleocapsid protein of SARS-CoV-2. It received EUA by the FDA in March 2020 22

and was available in our laboratory in April 2020. It has been demonstrated to have 99.9% 23 specificity and 100% sensitivity for detecting the IgG antibody in patients seventeen days or 24 more after symptom onset. 8 As per manufacturer instructions, a signal/cut-off (S/CO) ratio of 25 greater than or equal to 1.4 was interpreted as reactive, and an S/CO ratio of less than 1.4 was 26 interpreted as non-reactive. The change in this index value over time was measured from the 27 time of PCR diagnosis for each individual. This work was exempt from local Institutional 28

Review Board approval. 29

In a population of thirty residents in a single long-term care unit who were all negative by PCR 31 at baseline, twenty-four were infected with COVID-19 during the month of April 2020. All 32 residents had at least one clinical symptom at the time of diagnosis by PCR. Hospitalization was 33 required in 11 (46%), and 8 (33%) died. 34

Of these twenty-four COVID-19 positive patients, fifteen had antibody testing performed 35 sometime during the six-month period of the study; nine were unavailable for testing. The six 36 residents not diagnosed with COVID-19 did not have clinical symptoms of COVID-19 infection 37 and had negative PCR tests; all also had negative antibody testing. 38

Among the fifteen COVID-19 positive residents with antibody testing performed, three had tests 39 in one to six days from the time of infection diagnosis and all three had negative results. By days 40 seven to fourteen, all residents who were tested had antibodies detected. By six months, ten out 41 of eleven residents tested still had detectable antibodies, although the index value was lower for 42 all. There were two veterans who were immunosuppressed who continued to have detectable 43 antibodies at six months. The one patient that had waning antibody response at five months and a 44 of fever. The pattern of antibody values is shown in figure 1 . Every resident followed a similar 46 pattern, with peak response at thirty to forty-five days and declining response after that.

The SARS-CoV-2 IgG assay is helpful in identifying recent or prior COVID-19 infection. At this 49 time, it is unknown how long antibodies persist following infection. In this population of long-50 term care residents, we found that 91% still had IgG seropositivity at six months, albeit with 51 lower titers over time. Others have shown that individuals with mild or asymptomatic infection 52 develop less robust antibody responses, possibly accounting for the one patient that lost 53 seropositivity at six months. 9 The durability of response to natural infection in this vulnerable 54 population clearly wanes over time, further magnifying the importance of the large vaccination 55 efforts currently underway. 56

The authors report no conflicts of interest 58 

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