RESUMEN
Background: The reported infection rates, and the burden of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in low- and middle-income countries, including sub-Saharan Africa, are relatively low compared to Europe and America, partly due to limited testing capabilities. Unlike many countries, in Tanzania, neither mass screening nor restrictive measures such as lockdowns have been implemented to date. The prevalence of SARS-CoV-2 infection in rural mainland Tanzania is largely unknown. Methods: Between April and October 2021, we conducted a cross-sectional study to assess anti-SARS-CoV-2 seroprevalence among mother-child pairs (n=634 children, n=518 mothers) in a rural setting of north-eastern Tanzania. Findings: We found a very high prevalence of anti-SARS-CoV-2 antibody titres 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 in 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. Interpretations: The SARS-CoV-2 transmission 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 a load of communicable diseases may mask COVID-19. Surveillance could be implemented in tandem with the intensification of vaccination strategies.
RESUMEN
BACKGROUND: African countries stand out globally as the region seemingly least affected by the COVID-19 pandemic, caused by the virus SARS-CoV-2. Besides a younger population and potential pre-existing immunity to a SARS-CoV-2-like virus, it has been hypothesized that co-infection or recent history of Plasmodium falciparum malaria may be protective of COVID-19 severity and mortality. The number of COVID-19 cases and deaths, however, may be vastly undercounted. Very little is known about the extent to which the Tanzanian population has been exposed to SARS-CoV-2. Here, we investigated the seroprevalence of IgG to SARS-CoV-2 spike protein in two Tanzanian rural communities 1½ years into the pandemic and the association of coinciding malaria infection and exposure. METHODS: During a malariometric survey in July 2021 in two villages in north-eastern Tanzania, blood samples were taken from 501 participants (0-19 years old). Malaria was detected by mRDT and microscopy. Levels of IgG against the spike protein of SARS-CoV-2 were measured by ELISA as well as IgG against five different antigens of P. falciparum; CIDRα1.1, CIDRα1.4 and CIDRα1.5 of PfEMP1 and GLURP and MSP3. RESULTS: The seroprevalence of SARS-CoV-2 IgG was 39.7% (106/267) in Kwamasimba and 32.5% (76/234) in Mkokola. In both villages the odds of being seropositive increased significantly with age (AOR = 1.12, 95% CI 1.07-1.17, p < 0.001). P. falciparum malaria prevalence by blood smear microscopy was 7.9% in Kwamasimba and 2.1% in Mkokola. 81.3% and 70.5% in Kwamasimba and Mkokola, respectively, showed recognition of minimum one malaria antigen. Residing in Kwamasimba was associated with a broader recognition (AOR = 1.91, 95% CI 1.34-2.71, p < 0.001). The recognition of malaria antigens increased significantly with age in both villages (AOR = 1.12; 95% CI 1.08-1.16, p < 0.001). Being SARS-CoV-2 seropositive did not associate with the breadth of malaria antigen recognition when adjusting for age (AOR = 0.99; 95% CI 0.83-1.18; p = 0.91). CONCLUSION: More than a third of the children and adolescents in two rural communities in Tanzania had antibodies to SARS-CoV-2. In particular, the adolescents were seropositive but being seropositive did not associate with the status of coinciding malaria infections or previous exposure. In Tanzania, natural immunity may have developed fast, potentially protecting a substantial part of the population from later variants.