High seroprevalence of anti\SARS\CoV\2 antibodies in Chelsea, Massachusetts. persons 18C64 years and 65 years. Contamination\attributed immunity also increased in older\age groups. Wide ranges in seroprevalence GSK1838705A rates were noted across areas in March and June. The GSK1838705A highest seroprevalence rates were recorded GSK1838705A in Piraeus (47.2%) and West Attica (37.5%). However, the highest increase ( 5 occasions) occurred in Piraeus and the South Section of Athens, which are among the most densely populated areas in Athens. In both study periods, history of COVID\19 or febrile episode, and using a cohabitant with COVID\19 were associated with increased risk for seropositivity among unvaccinated persons (values 0.001 for all those comparisons). Table 2 Seroprevalence rates against SARS\CoV\2 according to characteristics of tested persons regardless of history of COVID\19 vaccination, March and June 2021 valuevalues 0.001 for all those comparisons). Age, gender, and area of residence were not associated with increased risk for seropositivity in March, regardless of history of COVID\19 vaccination. Table 3 Seroprevalence rates against SARS\CoV?2 according to characteristics of tested persons with no history of COVID?19 vaccination, March and June 2021 valuevalue 0.001). The following factors were significantly associated with increased risk for seropositivity: age (value 0.001), history of COVID\19 (value 0.001), history of febrile episode (value?=?0.011), using a cohabitant with a history of COVID\19 (value?=?0.001), and area of residence (values 0.001 for all those comparisons). In contrast, age and gender were not associated with increased risk for seropositivity. 3.3. Evolution of the third COVID\19 pandemic wave in the Athens metropolitan area Persons 18 years old had the highest seroprevalence rates attributed to natural SARS\CoV\2 contamination MSK1 in both studied periods (16.3% in March and 31.6% in June) (Table ?(Table3).3). In contrast, serologically confirmed immunity against SARS\CoV\2 was mainly vaccine\induced in persons 18C64 years and 65 years (Tables ?(Tables22 and ?and3).3). Nevertheless, seroprevalence attributed to natural SARS\CoV\2 contamination also increased during the third pandemic wave in older\age groups (Table ?(Table33). Wide ranges in seroprevalence rates against SARS\CoV\2 attributed GSK1838705A to natural infection were noted across studied areas (Table ?(Table3).3). In March 2021, West Attica had the highest seroprevalence rates against SARS\CoV\2 (14.3%) attributed to natural infection (Table ?(Table3).3). In June 2021, the highest seroprevalence rate among unvaccinated persons was noted in Piraeus (47.2%), followed by West Attica (37.5%). However, the highest increase of seroprevalence due to natural SARS\CoV\2 contamination was recorded in the South Section of Athens and Piraeus (5.5 and 5.18 times, respectively). 4.?DISCUSSION We conducted a two\point seroprevalence survey in March and June 2021 to study the evolution of the third COVID\19 pandemic wave in the Athens metropolitan area, which is mostly urban, with significant variations in population density and socioeconomic status of residents. To the best of our knowledge, this is among the few prospectively conducted seroepidemiological surveys not focusing on risk groups, and the only one conducted in the third pandemic wave, after the implementation of mass COVID\19 vaccination programs. Seroprevalence surveys at the regional level can yield valuable insights to guide future intervention GSK1838705A guidelines but also prepare the healthcare system. This is imperative given the emergence of new variants, the upcoming influenza season, and the suboptimal COVID\19 vaccine uptake rates in Greece, which can fuel additional waves of severe cases, hospitalizations, and deaths. 22 We estimated that this seroprevalence rate against SARS\CoV\2 increased sharply from 11.6% in March 2021 to 55.7% in June 2021. In particular, we estimated that approximately 435?208 residents in Athens had serologic evidence of immunity in March. This number was raised fivefold (to 2?082?568 residents) within a period of 3 months. This evolution is mainly attributed to the fast pace of the national vaccination program, which should be maintained until the vast majority of the population is vaccinated. High (31.5%) seroprevalence rates after the first pandemic wave were detected in the urban area of Chelsea, Massachusetts. 23 In contrast, negligible seroprevalence rates ( 0.5%) against SARS\CoV\2 were estimated after the first pandemic wave in Greece, which is attributed to the early implementation of nationwide lockdown. 24 In our study, although half of the seropositive cases in March were linked to natural infection, serologically proved immunity was mainly vaccine\driven in June. At that time, mass vaccination campaigns targeting all persons 25 years aged were fully implemented across the.
