SARS-CoV-2 outbreak in a synagogue community: longevity and strength of anti-SARS-CoV-2 IgG responses

Abstract

Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) pandemic is still ongoing along with the global vaccination efforts against it. Here, we aimed to understand the longevity and strength of anti-SARS-CoV-2 IgG responses in a small community (n = 283) six months following local SARS-COV-2 outbreak in March 2020. Three serological assays were compared and neutralisation capability was also determined. Overall 16.6% (47/283) of the participants were seropositive and 89.4% (42/47) of the IgG positives had neutralising antibodies. Most of the symptomatic individuals confirmed as polymerase chain reaction (PCR) positive during the outbreak were seropositive (30/32, 93.8%) and 33.3% of the individuals who quarantined with a PCR confirmed patient had antibodies. Serological assays comparison revealed that Architect (Abbott) targeting the N protein LIASON® (DiaSorin) targeting the S protein and enzyme-linked immunosorbent assay (ELISA) targeting receptor binding domain detected 9.5% (27/283), 17.3% (49/283) and 17% (48/283), respectively, as IgG positives. The latter two assays highly agreed (kappa = 0.89) between each other. In addition, 95%, (19/20, by ELISA) and 90.9% (20/22, with LIASON) and only 71.4% (15/21, by Architect) of individuals that were seropositive in May 2020 were found positive also in September. The unexpected low rate of overall immunity indicates the absence of un-noticed, asymptomatic infections. Lack of overall high correlation between the assays is attributed mainly to target-mediated antibody responses and suggests that using a single serological assay may be misleading.

Keywords: Herd immunity; IgG antibodies; SARS-CoV-2; neutralising antibodies; sero-prevalence.

Fig. 1.

Comparison between the serological assays used in this study. (a) Venn diagram representing sero-positivity of the different assays. (b) 2 × 2 tables of the three serological assays. Presented are the number of patients positive or negative for any two assays. Kappa values were: 0.58, 0.56, and 0.89 for Architect and LIASON, Architect and RBD-ELISA and LIASON and RBD-ELISA, respectively.

Fig. 2.

Segregation of positive results between serological and PCR assays. (a) The cumulative number of PCR positive and negative results in each serological assay. (b) Serological verdict based on the results of the serological and PCR assays.

Fig. 3.

Longevity of IgG 6 months compared to 2 months following the outbreak. Presented in the % of positive results in samples taken 6 months versus 2 months following exposure as detected by the different assays.