Rapid increase of SARS-CoV-2 seroprevalence during the 2020 pandemic year in the population of the city of Tirana, Albania

Abstract

Introduction: While the identification of anti SARS-CoV-2 antibodies has been used to measure the hidden circulation of the COVID-19 in communities, there are few publications on the dynamics of SARS-CoV-2 seroprevalence during both waves of 2020. This study provides original data about the change in proportion of individuals showing immune response to COVID-19 between beginning of July and end of December 2020. Methods: The study was conducted in two rounds, 27 June -3 July, and 21-28 December 2020, using two independently selected samples of individuals 20-70 years old. Study participants were randomly selected from lists of the inhabitants of the catchment communities of four primary health care centers in Tirana City. Serological testing was performed by an ELISA method which determines IgG class antibodies anti S1 protein of SARS-CoV-2 virus. The validity of the method was tested in a sample of blood donors sera of 2018. Results: The proportion of individuals classified as seropositive during the first round, in early July was 7.5% (95% CI: 4.3% - 10.7%). The proportion rose sharply in the second round, by late December 2020, reaching 48.2% (95% CI: 44.8% - 51.7%). The same increasing pattern was observed in all studied categories. No statistical significance was found between men and women and between age categories. The prevalence of seropositive individuals was always significantly higher among those who reported symptoms and those who had done the molecular test. Conclusion: The ratio of total infected cases over confirmed cases was estimated to be higher than 10 to 1 in Albania. The rapid increase in SARS-CoV-2 seroprevalence observed in Tirana City may have been facilitated by a number of factors, including the very low infection exposure during the period March - May 2020, and the consecutive high susceptibility in population. Despite the observed high seroprevalence, one month after the study, COVID-19 incidence continued to increase in Tirana.

Estimating the seroprevalence of SARS-CoV-2 antibodies: Understanding population-level immunity in Albania at the end of the Alpha variant wave

“…They also help characterize the factors that contributed to immunity status in this understudied population. These data contrast with prior seroprevalence information we have reported from one year earlier in June-July 2020, and in December 2020, before the Alpha variant surge in Albania; we found using the same methodology seroprevalence rates of 7.5% and 48.2%, respectively [ 4 ]. A recent study conducted among health care workers in Albania between February and May 2021 has found a seroprevalence of 72% [ 5 ].…”

“…ly [4]. A recent study conducted among health care workers in Albania between February and May 2021 has found a seroprevalence of 72% [5].…”

Primary Series COVID-19 Vaccine Effectiveness Among Health Care Workers in Albania, February–December 2021

“…This study of COVID-19 VE among HCWs in Albania, which -to the authors' knowledge -is the first COVID-19 VE study in an upper middleincome country in Europe, found moderate VE against PCR-confirmed COVID-19 among HCWs, most of whom had received two doses of BNT162b2 vaccine, during the Delta-predominant period. In contrast [20][21][22] , HCWs in this study had a high rate of prior infection only 1 year after the start of the pandemic, consistent with trends among HCWs in the Eastern European region, as well as high seroprevalence among the general population in Albania at this time [23] . In this population of previously infected HCWs, VE against COVID-19 was also moderate.…”

COVID-19 vaccine effectiveness among healthcare workers in Albania (COVE-AL): protocol for a prospective cohort study and cohort baseline data

“…The enrolment profile of participants in our study offers unique challenges and opportunities. Over 70% of our study participants were seropositive for SARS-CoV-2 anti-spike antibodies on enrolment, a figure that is higher than the 48% seropositivity reported from a seroprevalence survey of the general population of Tirana, Albania during December 2020,23 which was nearly 2 months prior to the start of our study. Nearly all (98%) vaccinated participants had serology drawn within 4 days of their first vaccination, making it very unlikely that this seropositivity reflects a vaccine-induced antibody response.…”