A deadly disease has emerged. There is no known treatment. Public opinion is split on how to tackle the outbreak. Those words could apply to the COVID-19 pandemic. In fact, they also apply to the yellow fever outbreak that swept through America’s capital city not long after the American Revolution. The 1793 episode shows us that the medical response to a crisis is easily politicized.

Yellow fever is a viral disease that’s spread by mosquitoes. It often causes jaundiced or yellowed skin (hence its name), vomiting, bleeding and death. In the late summer of 1793, refugees from a yellow fever epidemic in the Caribbean fled to Philadelphia, which was then the capital city of the young United States of America. Their ships unfortunately also carried Aedes aegypti mosquitoes—vectors of the yellow fever virus.

Within months, 11,000 people, or 20 percent of Philadelphia’s population at the time, contracted the disease. Of that number, around 5,000 people or 45 percent died. That amounted to about 10 percent of Philadelphia’s total population.

For comparison, the World Health Organization has estimated that the fatality rate for COVID-19 is 3.4 percent and a study in the British medical journal The Lancet suggested the fatality rate to be 3 percent. Other estimates claim that the fatality rate is much lower than that. While experts are still unsure of the true fatality rate of the current pandemic, no research suggests it to be anywhere near what the Philadelphians endured in 1793.

Philadelphia’s yellow fever epidemic understandably created a mass panic in the capital and prompted 17,000 people, including President George Washington and many other government officials, to leave the city and seek refuge in the countryside.

Dr. Benjamin Rush, one of the signers of the Declaration of Independence, chose to remain in the city and tirelessly tended to the sick. It is said that he sometimes visited a hundred patients in a single day.

Unfortunately, medicine was still primitive and many of Rush’s treatments were counterproductive. They included bloodletting and prescribing calomel (i.e. toxic mercury chloride). Rush believed that his methods saved his own life from the illness. For most patients, however, Rush’s interventions almost certainly did more harm than good.

Another Founding Father who chose to remain in Philadelphia was the then Secretary of the Treasury, Alexander Hamilton. Hamilton and his wife survived the disease and he attributed their recovery to comparatively mild treatments, including the quinine-rich bark of the cinchona tree. It is now known that quinine, a stimulant and malaria treatment, does not destroy the yellow fever virus. But it may have acted as a placebo.

The question of yellow fever treatment quickly became political. Rush was a member of the Democratic-Republican Party, while Hamilton was a Federalist. Whether one favored mercury and bloodletting or milder treatments such as cinchona bark became a partisan issue.

Which treatments Philadelphians read about depended on their preferred media outlet. The Federalist-sympathizing Gazette of the United States exclusively printed medical recommendations from Hamilton’s favored physician. The ostensibly impartial Federal Gazette overwhelmingly published Rush’s advice and omitted conflicting viewpoints.

The cause of the illness was also a partisan matter. The Democratic-Republicans believed that the disease was local in origin, while the Federalists blamed the recent refugees and their ships. “More than one-third of the most prominent national and local political leaders in Philadelphia took a public position on the cause of the epidemic,” according to University of Michigan historian Martin Pernick. “With few exceptions the [Democratic-]Republicans backed a domestic source of the fever, while Federalists largely blamed importation.”

In that climate of extreme politicization, little progress was made toward finding an effective treatment. In the end, the yellow fever outbreak was defeated by luck—a cold winter killed off the disease-carrying mosquitoes and ended the epidemic. Over the years, as ships brought in more mosquitoes from abroad, other outbreaks of yellow fever flared up occasionally in coastal U.S. cities. A vaccine would not come into use until 1938.

As the country combats the current pandemic, we should refrain from politicizing the issue and evaluate available treatments based solely on scientific evidence. Unfortunately, health policy discussions are often driven by party loyalty rather than evidence. Polling shows that opinions on the seriousness of the pandemic have become divided along partisan lines.

Early on, President Donald Trump dismissed the threat posed by COVID-19, and Republicans remain considerably less worried about the virus than Democrats. Nowadays, it is the Democrats who stand in the way of more rapid re-opening of the economy pushed by the Republicans. Of course, the true death rate of the novel coronavirus is still being studied, and hopefully political pressures will not hamper the search for the objective truth, whatever it may be.

Treatments for COVID-19 have also become politicized. Remdesivir, a drug that combats Ebola, and hydroxychloroquine, an anti-malaria drug, are both being studied as possible COVID-19 treatments. In both cases, we have some initial ideas about their effectiveness, but more trials are needed to assess their efficacy against COVID-19. Yet partisan fighting about hydroxychloroquine has slowed down the process of determining the truth about that drug’s effectiveness against COVID-19. Let’s hope that similar pressures do not hamper further investigation of Remdesivir.

As another example of politicization, consider the use of ultraviolet light against the virus. The method involves intermittently shining ultraviolet light through an endotracheal catheter, and is being explored as a potential treatment for coronavirus and other respiratory infections. After President Trump’s seeming endorsement of the technique, there has been a considerable backlash against ultraviolet light therapies. Under pressure from political activists, YouTube and Vimeo removed videos about the experimental treatment, which is being studied at Cedars-Sinai Medical Center in Los Angeles. Similarly, Twitter suspended the account of a biotechnology company behind the new therapy.

The research is still in an early phase, but it should not be dismissed purely on partisan grounds—whatever the current president’s opinion on the subject.

We should not allow politics to drive what we believe about the virus or the best medical response, instead reviewing the available evidence with an open mind. Reflexively supporting or opposing a particular medical approach because of the endorsements of politicians makes no sense.

The novel coronavirus pandemic may feel unprecedented, but of course humanity has dealt with the horrors of plagues and epidemics throughout history. As humanity tackles the serious, global problems presented by the current pandemic, we should learn the lessons of the past and know that beating COVID-19 will require clear heads and a reliance on reason and data.

Chelsea Follett is a policy analyst at the Cato Institute.