Antibody seroprevalence against SARS-CoV-2 within the Canton of Sarajevo, Bosnia and Herzegovina-One year later

Abstract

Background: Serostudies are important resources when following pandemics and predicting their further spread, as well as determining the length of protection against reinfection and vaccine development. The aim of this study was to update data on the prevalence of seropositive individuals in Canton Sarajevo, Bosnia and Herzegovina (B&H) from September 2020 to May 2021.

Methods: Anti-SARS-CoV-2 antibodies were quantified using an electrochemiluminescence immunoassay.

Results: Compared to the period April-July 2020, when anti-SARS-CoV-2 antibodies were detected in 3.77% of samples, one year later (May 2021) the estimated percentage within the same population of the urban Canton Sarajevo was 29.9% (5,406/18,066). Of all anti-SARS-CoV-2 Ig-positive individuals, 53.27% were men, and 69.00% were of 50 years of age or younger. Also, the current update found the individuals 50 years of age or younger to be more frequently anti-SARS-CoV-2 Ig positive compared to older individuals. On the other hand, higher median anti-SARS-CoV-2 Ig levels were found in individuals > 50 years old than in younger individuals, as well as in men compared to women. Seropositivity gradually increased from September 2020 to May 2021, with the lowest frequency of positive cases (3.5%) observed in September 2020, and the highest frequency (77.7%) in January 2021.

Conclusion: Our results provided important seroprevalence data that could help in planning restrictive local public health measures to protect the population of Sarajevo Canton, especially considering that at the time of the study the vaccines were virtually inaccessible to the general population not belonging to any of the high-priority groups for vaccination.

Fig 1. Effects of age on the frequency of positive cases.

A total of 69.02% of the individuals who tested positive were of 50 years of age or younger, while 30.98% were > 50 years old, and the chi-square test revealed this association between the proportion of positive cases and two age groups to be significant (X² = 10.274; df = 1; p = 0.001).

Fig 2. Effect of age on median anti-SARS-CoV-2 Ig levels.

Significantly higher median anti-SARS-CoV-2 Ig level was found in the individuals > 50 years old when compared to the younger group (25.9; IQR 59.00 vs 16.00, IQR 36.00; U = 2535473.00; p < 0.001).

Fig 3. Effects of sex on the frequency of positive cases.

A total of 2,880 (53.27%) anti-SARS-CoV-2 Ig-positive individuals were men, while 2,526 (46.72%) were women, the chi-square test revealed no significant association between the proportion of positive cases and gender (X² = 2.890; df = 1; p = 0.090).

Fig 4. Effects of sex on median anti-SARS-CoV-2 Ig levels.

The median anti-SARS-CoV-2 Ig level among individuals who tested positive was 18.9, interquartile range 43.9. Significantly higher median anti-SARS-CoV-2 Ig level was found in men when compared to women (20.40, IQR 49.72 vs 17.3, IQR 38.7; U = 3365817.50; p < 0.001).

Fig 5. Mean age among positive female and male participants.

The mean age of all individuals who tested positive was 43.21 ± 14.91. Mean age did not differ significantly between men (43.51 ± 14.99) and women (42.86 ± 14.82) who tested positive (t test = 1.589; p = 0.112).

Fig 6. The frequency of positive cases throughout a nine-month time frame.

The lowest frequencies of positive cases were observed in September 2020 (3.5%, 84/2,376) and October (5,4%, 82/1,509) 2020 while the highest frequencies were observed in January 2021 (77.7%, 483/622), and in April 2021 (60.1%, 1,042/1,734).