Revisiting a COVID-19 seroprevalence cohort survey among health care workers and their household members in Kinshasa, DR Congo, 2020-2022

Serological surveys provide the most direct measurement to define the immunity landscape for many infectious diseases, including COVID-19, yet this methodology remains underexploited to clarify transmission dynamics. This is specifically the case in the context of the Democratic Republic of Congo, where COVID-19 case presentation was apparently largely oligo- or asymptomatic, and vaccination coverage remained extremely low. A cohort of 635 health care workers from 5 health zones of Kinshasa and 670 of their household members was followed up between July 2020 and January 2022, with 6- to 8-week intervals in the first year and 4- and 8-month intervals in the last year. At each visit, information on risk exposure and a blood sample were collected. Serology was defined as positive when binding antibodies against SARS-CoV-2 spike and nucleocapsid proteins were simultaneously present. The anti-SARS-CoV-2 antibody seroprevalence was high at baseline, at 17.3% (95% CI 14.4–20.6) and 7.8% (95% CI 5.5–10.8) for health care workers and household members, respectively, and fluctuated over time, between 9% and 62.1%. Seropositivity was heterogeneously distributed over the health zones (p < 0.001), ranging from 12.5% (95% CI 6.6–20.8) in N’djili to 33.7% (95% CI 24.6–43.8) in Bandalungwa at baseline for health care workers. Seropositivity was associated with increasing rounds aOR 1.75 (95% CI 1.66–1.85), with increasing age aOR 1.11 (95% CI 1.02–1.20), being a female aOR 1.35 (95% CI 1.10–1.66) and being a health care worker aOR 2.38 (95% CI 1.80–3.14). There was no evidence that health care workers brought the COVID-19 infection back home, with increased seropositivity risk among household members in subsequent surveys. There was much seroreversion and seroconversion detected over the different surveys, and health care workers had a 40% lower probability of seroreverting than household members (aOR 0.60 (95% CI 0.42–0.86)). Based on the WHO guidelines on the potential use of sero-surveys, the results of this cohort were revisited, and evidence provided by such studies in a ‘new disease’ epidemic and in a setting with low molecular testing capacities, such as COVID-19 in DRCongo, was insufficient to guide policy makers for defining control strategies.