Understanding COVID-19 Epidemiology and Implications for Control: The Experience from a Greek Semi-Closed Community

Abstract

Background: We aimed to estimate the SARS-CoV-2 antigen and antibody seroprevalence in one of the worst-affected by the pandemic semi-closed communities in Greece, Deskati, and evaluate the sociodemographic and clinical correlations of functional antibody responses. Methods: The Ag2019n-CoV V1310/V1330 Rapid Test (Prognosis Biotech, Greece) was used for antigen detection. The Rapid Test 2019-nCoV Total Ig, V1210/V1230 (Prognosis Biotech, Greece), and the SARS-CoV-2 IgG II Quant method (Architect, Abbott, Illinois, USA) were used for antibody testing. Results: None of the participants had a positive antigen result. SARS-CoV-2 seropositivity ranged from 13% to 45% in the study population, depending on the method. One-third of the participants with known past infection had a positive antibody test result 77 ± 13 days after infection. Two-fifths of infections determined by serology were asymptomatic. The advancing age and hospitalization predicted seropositivity among patients with past infection. Half of the participants who tested positive for antibodies were not aware of past infection. Conclusions: High-burden contexts in Greece, such as Deskati, are not so far from herd immunity thresholds. We highlighted the value of low-cost serosurveys targeting both symptomatic and asymptomatic populations to evaluate the natural immune response to SARS-CoV-2 in nonvaccinated susceptibles and design evidence-based policies for lifting lockdowns.

SARS-CoV-2 Sero-Surveillance in Greece: Evolution over Time and Epidemiological Attributes during the Pre-Vaccination Pandemic Era

“…Seroprevalence in Greece evolved over time and varied across geographic regions and between metropolitan/non-metropolitan areas, with regional units encompassing the cities of Athens and Thessaloniki showing an approximate two-fold increase in seropositivity. Our present work extends from our previously published seroprevalence survey reports, and is in accordance with the limited number of published studies from Greece in high-risk populations, specifically considering health care workers, transmission hot spots or other unique groups such as blood donors [ 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. These studies all addressed earlier stages of the COVID-19 pandemic.…”

Lessons We Have Learned Regarding Seroprevalence in High and Low SARS-CoV-2 Contexts in Greece before the Omicron Pandemic Wave

“…In our previous studies, we showed that SARS-CoV-2 seropositivity approached 45% in high-burden contexts of COVID-19 in Greece after the easing of measures during the second pandemic wave in November 2020, which was exclusively attributed to humoral immunity [2]. Notably, when the vaccination strategy was included nine months after this pandemic wave, SARS-CoV-2 seropositivity was increased to 76% [3].…”

Defining Antibody Seroprevalence and Duration of Humoral Responses to SARS-CoV-2 Infection and/or Vaccination in a Greek Community

“…A serosurveillance program was conducted in the municipality of Deskati on 6 June 2021 to investigate the duration of antibody responses to SARS-CoV-2 infection and/or vaccination five months after an initial serosurveillance study [ 8 ] and nine months after the initiation of the pandemic wave in the area (October 2020). All the residents of Deskati who had been recruited to the first serosurveillance program (conducted in January 2021 [ 9 ]) were invited to participate in the follow-up program by the local authority and had been notified of the time and place thereof. Participants were recruited by announcing the research in the media while local officials organized a one-month recruitment campaign.…”

“…The SARS-CoV-2 IgG II Quant ELISA method (Architect, Abbott, IL, USA), a chemiluminescent microparticle immunoassay, was used for the qualitative and quantitative determination of IgG antibodies against the spike receptor-binding domain (RBD) of SARS-CoV-2 in serum specimens [ 8 ], with a sensitivity of 99.9% and specificity and 100% for detecting the IgG antibodies generated by prior infection or vaccination, as previously described [ 9 , 10 ].…”