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

BACKGROUND: Nation-wide SARS-CoV-2 seroprevalence surveys provide valuable insights into the course of the pandemic, including information often not captured by routine surveillance of reported cases. METHODS: A serosurvey of IgG antibodies against SARS-CoV-2 was conducted in Greece between March and December 2020. It was designed as a cross-sectional survey repeated at monthly intervals. The leftover sampling methodology was used and a geographically stratified sampling plan was applied. RESULTS: Of 55,947 serum samples collected, 705 (1.26%) were found positive for anti-SARS-CoV-2 antibodies, with higher seroprevalence (9.09%) observed in December 2020. Highest seropositivity levels were observed in the "0-29" and "30-49" year age groups. Seroprevalence increased with age in the "0-29" age group. Highly populated metropolitan areas were characterized with elevated seroprevalence levels (11.92% in Attica, 12.76% in Thessaloniki) compared to the rest of the country (5.90%). The infection fatality rate (IFR) was estimated at 0.451% (95% CI: 0.382-0.549%) using aggregate data until December 2020, and the ratio of actual to reported cases was 9.59 (7.88-11.33). CONCLUSIONS: The evolution of seroprevalence estimates aligned with the course of the pandemic and varied widely by region and age group. Young and middle-aged adults appeared to be drivers of the pandemic during a severe epidemic wave under strict policy measures.

Factors associated with IgG positivity to Crimean-Congo hemorrhagic fever virus in the area with the highest seroprevalence in Greece.

In order to gain insight into the factors playing a role for the high seroprevalence of Crimean-Congo hemorrhagic fever virus in the human population of Thesprotia prefecture, Greece, serum samples were collected from residents of the area together with a questionnaire about demographic and epidemiological factors. A 14.4% seroprevalence was detected, with increased age, agro-pastoral activities, slaughtering, and contact with animals (especially sheep) among the factors associated with seropositivity. The high seroprevalence with the absence of any clinical cases needs further investigation.