Africa’s low COVID-19 infection rate and death toll have mystified health experts throughout the pandemic.

Despite comprising nearly 20 percent of the world’s population, the continent has reported only 2 percent of global COVID-19 cases and 4 percent of global COVID-19 deaths since the start of the pandemic. Some have theorized that Africa’s younger population, lack of testing capacity, exposure to other infections, and asymptomatic cases, may contribute to underestimated COVID-19 infection and mortality tolls, but these possibilities remain unclear.

School of Public Health researchers are seeking to unravel this mystery and gain a better understanding of COVID-19 risk and transmission in Africa, thanks to a $3.3 million grant from the National Institute of Allergy and Infectious Diseases.

Clarissa Valim, research associate professor of global health, and Patricia Hibberd, chair and professor of global health, are principal investigators of the award, which totals $3,338,146 over five years. Valim and Hibberd will study COVID-19 infection and transmission in the southeastern country of Malawi, where only 1.5 percent of the population has received the COVID-19 vaccine. Davidson Hamer, professor of global health at SPH and professor of medicine at the School of Medicine (MED), and Suryaram Gummuluru, professor of microbiology at MED, are also members of the research team.

“COVID-19 was expected to have a devastating impact in sub-Saharan Africa because of overcrowding in cities, poor sanitation and vulnerable healthcare systems,” Valim says. “The presence of other significant infections such as HIV, tuberculosis, and malaria, combined with undernutrition, was expected to increase the risk of severe infection. However, these predictions do not seem to have materialized.”

For the new study, the researchers will assess innate and acquired immunity to the virus over time, in both vaccinated individuals and those naturally infected with COVID-19.

The team will examine COVID-19 risk and predictors among 1,200 vaccinated and unvaccinated participants in Malawi, ranging from 5 to 75 years old. Focusing on household transmission, they will explore whether innate immune responses lower the risk of COVID-19 infection, and whether these responses are associated with other infections and conditions common in the region, including malaria, chronic malnutrition, and anemia. They will also investigate whether this exposure affects antibody levels in vaccinated and unvaccinated individuals.

“Our study focuses on the high burden of other infections, particularly parasites, in patients with COVID-19,” Valim says. “We are studying whether repeated exposures to malaria, intestinal parasites, and other pathogens result in long-lasting changes in the innate immune system that facilitate a more rapid and enhanced immune response to COVID-19, and limit progression of symptoms and vaccine-induced immune responses.”

The study results will be compared with COVID-19 data in North America and Australia. The researchers hope their findings will inform cost-effective and efficient vaccination programs and policies in sub-Saharan Africa, particularly to protect high-risk populations.

“If we observe lower incidence rates of COVID-19 morbidity in Malawi, lower rates of vaccination might effectively control virus transmission and mortality,” says Valim. “On the other hand, if susceptible people acquire short-lived immunity after infection or vaccination, booster doses may be needed at shorter intervals.”