More than two years into the Covid-19 pandemic, the social, economic and political implications of public health crises are more apparent than ever—as is the fact that people of color and poorer communities often bear the brunt of these contagions’ consequences.

A new analysis of yellow fever in antebellum New Orleans highlights striking parallels with the ongoing pandemic, illustrating how the mosquito-borne virus interacted with the Louisiana capital’s unique climate, cotton-driven economy and violently exploitative labor regime to spark wave after wave of epidemics. Against a backdrop of intensifying slavery, yellow fever transformed New Orleans into a city of the dead, claiming as many as 150,000 lives between 1803 and the outbreak of the Civil War. The disease also created a horrific form of what Kathryn Olivarius, a historian at Stanford University, describes as “immunocapitalism”: a “socially acknowledged lifelong immunity to a highly lethal virus, providing access to previously inaccessible realms of ... power.”

In her book Necropolis: Disease, Power, and Capitalism in the Cotton Kingdom, out now from Harvard University Press, Olivarius explores the racialized nature of New Orleans’ yellow fever epidemic. For the disease-ridden city’s 19th-century populace, immunity was the key to opportunity, determining where locals lived and worked, who they socialized with, and other aspects of daily life. Because people had no way of proving their immunity in this pre-vaccine world, accruing “immunocapital” was more about convincing others of one’s status than actually being immune to yellow fever. This immunity—whether real or perceived—had wildly conflicting implications for white Orleanians and enslaved Black people.

At the time, medical professionals erroneously believed that African people were immune to yellow fever—a theory that was used, in turn, to justify racial slavery. Slaveholders reasoned that “God intended for enslaved people to be enslaved, specifically in the American South, ... because the cotton economy would entirely collapse without the labor of immune Black people,” says Olivarius. “Many pro-slavery theorists and doctors essentially were saying that Black slavery was positively humanitarian, because it distanced white people, who would be vulnerable to yellow fever, from labor and spaces that would kill them, whereas Black people could safely work in these spaces.”

Smithsonian chatted with Olivarius about yellow fever in New Orleans, how surviving the disease played out differently for white and Black people, and what it was like to write about the history of racism and disease in the midst of a pandemic. Read a condensed and edited version of the conversation below.

What is yellow fever, and how is it different from Covid-19?

Yellow fever is very, very different from Covid-19. It’s an acute hemorrhagic fever spread by mosquitoes, and in the 19th century and earlier, it was the most terrifying disease in the Atlantic world. This was the disease that kept people up at night, because it was a miserable way to die. Victims experienced a sudden onset of nausea and chills, muscle pains, back aches, and jaundice. Within days, patients would be oozing blood through their orifices. They vomited up partly coagulated blood with the consistency and color of coffee grounds. They could lapse into a coma and die of organ failure. Even the most pious victims—ministers, priests—were screaming profanities as the end neared. It was that painful.

Yellow fever was terrifying because it was so mysterious. Even the most experienced doctors were flummoxed. There was no cure, no inoculation, no satisfactory explanation for why it killed some people and spared others. It was only at the end of the 19th century that Cuban researchers discovered yellow fever’s vector, the female Aedes aegypti mosquito, and only in the 1930s that an effective vaccine was developed.