Dynamics and variant-specific patterns of SARS-CoV-2 reinfection in Ethiopia: A prospective longitudinal cohort study.

OBJECTIVES

This study aimed to assess the dynamics, risk factors, and variant context of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfection in Ethiopia.

METHODS

We conducted a longitudinal surveillance study in Jimma and Addis Ababa, Ethiopia, enrolling 1000 participants, with 957 eligible for reinfection analysis, between November 2022 and December 2024. Reinfection was defined by increases in anti-nucleocapsid antibody titers measured at 3-month intervals. SARS-CoV-2-positive samples underwent genomic sequencing. Reinfection risk was assessed using an interval-censored discrete-time survival model with a complementary log-log link.

RESULTS

After 12 months, 62.4% (597/957; 95% CI, 59.3-65.5%) had at least one reinfection. This increased to 86.6% (95% CI, 84.3-88.6%) at 24 months with an estimated cumulative reinfection probability of 95.3% (95% CI, 92.0-97.3%). Reinfection risk was higher in females (HR, 1.13; 95% CI, 1.01-1.27), participants from semi-urban Jimma compared with urban Addis Ababa (HR, 1.20; 95% CI, 1.06-1.38), and during the Belg season (a brief rainy season from March to May; HR, 1.49; 95% CI, 1.30-1.71). Prior SARS-CoV-2 infections were associated with lower reinfection risk: 25% reduction after one infection (HR, 0.75, 95% CI, 0.67-0.84) and 55% reduction after two or more infections (HR, 0.45, 95% CI, 0.37-0.55). Sequencing identified multiple Omicron sub-lineages (CH.1.1.18, JN.1.18, XBB.1.5, LY.1, and LB.1.3.1), without severe disease.

CONCLUSION

Reinfection was common over 24 months and was not associated with severe COVID-19. Risk varied by season, geography, and sex. Repeated infections appeared to confer cross-protective immunity against diverse Omicron sub-lineages.