High anti-SARS-CoV-2 seroprevalence among unvaccinated mother-child pairs from a rural setting in north-eastern Tanzania during the second wave of COVID-19

Background: The reported infection rates and burden of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in low- and middle-income countries, including those in sub-Saharan Africa, are relatively low compared to the rates and burden in Europe and America, partly due to limited testing capability. Unlike many countries, Tanzania has implemented neither mass screening nor restrictive measures such as lockdowns to date. The prevalence of SARS-CoV-2 infection in rural mainland Tanzania is largely unknown.

Methods: A cross-sectional study was conducted between April and October 2021 to assess the anti-SARS-CoV-2 seroprevalence among mother-child pairs (n = 634 children, n = 518 mothers) in a rural setting in north-eastern Tanzania.

Results: A very high prevalence of anti-SARS-CoV-2 antibody titres was found, with seroprevalence rates ranging from 29% among mothers and 40% among children, with a dynamic peak in seropositivity incidence at the end of July/early August being revealed. Significant differences in age, socioeconomic status, and body composition were associated with seropositivity in mothers and children. No significant associations were observed between seropositivity and comorbidities, including anaemia, diabetes, malaria, and HIV.

Conclusions: The transmission of SARS-CoV-2 in a rural region of Tanzania during 2021 was high, indicating a much higher infection rate in rural Tanzania compared to that reported in the UK and USA during the same period. Ongoing immune surveillance may be vital to monitoring the burden of viral infection in rural settings without access to molecular genotyping, where the load of communicable diseases may mask COVID-19. Surveillance could be implemented in tandem with the intensification of vaccination strategies.