Impact of a six-month COVID-19 travel moratorium on Plasmodium falciparum malaria prevalence on Bioko Island, Equatorial Guinea

Abstract Importation of malaria infections has long been suspected as a driver of sustained malaria prevalence on areas of Bioko Island, Equatorial Guinea. However, quantifying the impact of imported infections is difficult because of the dynamic nature of the disease and the complexity of designing a randomized trial. Here, we leverage a six-month travel moratorium in and out of Bioko Island during the initial COVID-19 pandemic response to evaluate the contribution of imported infections to Pf prevalence on Bioko Island. Using a difference in differences design and data from island wide household surveys conducted before (2019) and after (2020) the travel moratorium, we compared the change in prevalence between areas of low historical travel to those with high historical travel. We found that prevalence increased in low travel areas after the moratorium compared to before, while prevalence decreased in high travel areas. In the absence of a travel moratorium, the prevalence of infection in high travel areas was expected to be 5% higher than what was observed. The observed decrease in prevalence can be directly attributed to the lack of imported cases, highlighting the importance of control measures that target these types of infections.