Trends in SARS-CoV-2 seroprevalence in Albania during the 2021–2022 pandemic year

Background: Monitoring SARS-CoV-2 seroprevalence dynamics during the COVID-19 pandemic is crucial for understanding population immunity and providing insights into public health policies. Limited data exist on this from Albania and other Eastern European countries. This study aimed to investigate SARS-CoV-2 seroprevalence in Albania, comparing August 2021 and August 2022 data from two representative samples of the general population. The objective was to understand the temporal dynamics of SARS-CoV-2 antibodies across age groups and assess the impacts of natural infection and vaccination on population immunity. Methods: This longitudinal study was conducted in two consecutive cross-sectional assessments 12 months apart in Albania's urban all-ages population. IgG anti-Spike-1 and anti-Nucleoprotein SARS-CoV-2 antibodies were measured using ELISA, focusing on seropositivity rates and antibody levels. Methods: The study encompassed 2143 and 2183 individuals in August 2021 and 2022, respectively, with the anti-S1-IgG seropositivity rate escalating from 70.9 ​% to 92.1 ​%. In 2021, seroprevalence ranged from 49.6 ​% (0–15 years) to 82 ​% (>60 years). By August 2022, it surpassed 90 ​% in most age groups, except 0–15 years (73.8 ​%). ''Hybrid'' immunity (COVID-19+ and Vaccine+) reached 56.6 ​% in 2022, or 2.8 times higher than in 2021, exhibiting the highest antibody levels compared to the only vaccinated or previously COVID-19-infected individuals. Conclusion: This study highlights an overall 94 % seroprevalence in the Albanian population in August 2022 and robust ''hybrid'' immunity, suggesting substantial protective immunity against SARS-CoV-2. The lower immunity in the 0–15 age group underscores the necessity for youth-targeted vaccine campaigns. These findings provide valuable insights for shaping healthcare measures and vaccination policies.