NARRATION: The U.S. has joined other countries in looking to antibody testing as a key tool for economic revival.

ARCHIVAL (KRON, 4-12-20):DR. STEPHEN HAHN (FDA COMMISSIONER): We think it will be a tool to help us get people back to work.

ARCHIVAL (FOX, TOWN HALL, 5-3-20):PRESIDENT DONALD TRUMP: We want to go back to work quickly, but safely. And thats whats happening.

NARRATION: But thats created controversy.

ARCHIVAL (CNN, 4-20-20):DR. ASHISH JHA (DIRECTOR, HARVARD GLOBAL HEALTH INSTITUTE): There are a lot of tests out there creating lots of false positives.

DR. DAVID W. DOWDY (ASSOCIATE PROFESSOR, JOHNS HOPKINS BLOOMBERG SCHOOL OF PUBLIC HEALTH): We dont currently have a great test to tell if someone is immune or not. Just because they have antibodies does mean they are immune.

NARRATION: And even if perfected, these tests may create problems of their own.

KATHRYN OLIVARIUS (ASSISTANT PROFESSOR OF HISTORY, STANFORD UNIVERSITY): Its important to look back into history because we dont want the past to become prelude.

I. GLENN COHEN (BIOETHICIST AND LAW PROFESSOR, HARVARD UNIVERSITY): So imagine weve got great tests we believe are picking up immunity. Before we roll something out like this I think we have to be really sure that were going to take care of those left behind. The alternative is that we end up with a two-tier society where theres some people who are employable who can go out in public and others who dont have jobs, and who cant feed their family. And thats both unfair in terms of how we distribute goods in this society. But it also might have consequences for public health because it may incentivize people to go out and try to expose themselves to risks in order to have access to the economy and access to public life. And thats not something you want.

NARRATION: History shows that concern isnt just theoretical, says Stanford historian Kathryn Olivarius.

KATHRYN OLIVARIUS: Epidemics and pandemics provide any society great challenges. But the real danger is that these moments exacerbate all sorts of existing inequalities that we already have in our societies.

NARRATION: One example? The way some southern communities dealt with yellow fever in the 1800s.

KATHRYN OLIVARIUS: The disease reached epidemic proportions and this cast a much longer shadow than just mortality. Those who survived, now so-called acclimated citizens, their lives had been permanently transformed. Now you could get a job. There were certain people that you could marry. There were certain social networks that you could tap into. Banks were happier to extend you credit. All of these elements of life in the South were suddenly open to you. And so this became a pathway essentially to prosperity, a kind of prerequisite for having a job, a credential like having a university degree or having language skills. This was touted as the sort of Rubicon moment. But of course, it also created some very pernicious side effects. Epidemiological discrimination became one of many forms of discrimination that riddled society.

NARRATION: Acclimation governed everything from the price of slaves to the ability to get life insurance and newcomers would even seek out infection in the hopes of becoming immune to the disease.

KATHRYN OLIVARIUS: Ive seen examples of young men hopping into the beds of their recently dead friends. Theyre literally risking their lives seeking sickness is the pathway to prosperity.

NARRATION: Over time, instead of improving health care to decrease the death toll, the leaders of New Orleans came to see the recurring waves of yellow fever as little more than natural selection at work.

KATHRYN OLIVARIUS: The richest and most powerful all incorporated acclimation into their sort of genesis stories crafted as a demonstration of a persons manliness, of their worth, of their bravery, a sort of catchall statement of character. It becomes the attitude of the government, essentially that that the only solution to yellow fever is not expensive sanitation efforts. In fact, the solution to yellow fever is more yellow fever.

ARCHIVAL (FOX NEWS, 4-20-20):DAN PATRICK (TEXAS LT. GOV.) You know they told us, Tucker, to follow the science. Well, what science?

NARRATION: With frustration growing over the lengthy mitigation measures scientists say are necessary to combat Covid-19

ARCHIVAL (FOX17):WOMAN: I hate that we have to see each other as a disease now.

Narration: some pundits and U.S. policy makers are advocating that more people, not less, need to be infected.

ARCHIVAL (FOX NEWS, 4-19-20):DR. DAVID KATZ: Herd immunity is the best way to get to a place where grandparents can once again hug their grandchildren.

NARRATION: Herd immunity can occur when a critical mass of the population has been infected or vaccinated, helping to slow the viruss course.

ARCHIVAL (FOX NEWS, 4-9-20):MARK LEVIN: They tell you to hunker down. Tens of millions of Americans as a result of this mitigation that Dr. Fauci and Dr. Birx are focused on will not have developed any immunity to this.

NARRATION: But trying to gain herd immunity without a vaccine is very risky, says epidemiologist David Dowdy.

DR. DAVID W. DOWDY: What we do in the next one, two, three months should not be dictated by a desire to achieve herd immunity in the long term. So, the only way were going to get herd immunity to Covid-19 without a vaccine is for large proportions of the population to get sick again. More than half of the entire population would have to get infected in order to even approach herd immunity to this disease.

ANITA GUERRINI (HISTORIAN OF SCIENCE, OREGON STATE UNIVERSITY): Its not a good idea. In some ways we know less about coronavirus now than people knew about smallpox in the 18th century.

NARRATION: Back then, in order to gain immunity to smallpox, people would sometimes seek it out.

ANITA GUERRINI: If you knew someone who had a mild case of smallpox, you would get the scabs. You would grind them up. You would either snort them or more commonly, you would make a little cut in the arm and put some of that in and tie it up. And you would get the disease. Presumably it was a mild case, but it wasnt necessarily, and some people died from the inoculation. Thats directly comparable to having a coronavirus party because people will die from it.

NARRATION: For those who believe social distancing measures are preventing herd immunity to the coronavirus, the history of smallpox offers another lesson.

ANITA GUERRINI: Even when there was a vaccine, it took another almost two hundred years to achieve eradication, and that was by a very intensive vaccination program that ended in the 1970s. So, in terms of herd immunity for coronavirus, I think it would be very difficult to obtain without a vaccine.

NARRATION: And that was with a virus where exposure clearly provided long-term immunity to those lucky enough to survive.

ANITA GUERRINI: If the population in general were more informed about how infectious disease works, how we get sick that would definitely have an impact on our political response. We need to understand this a lot better than we do.

I. GLENN COHEN: I think when youre in a crisis, you grasp at straws and thats OK. But I think the more we are led by the public health experts and the less by ordinary politics, the better we will be. Theres a whole bunch of scientific history where we can learn about. The same kinds of things, especially the worrisome things, our tendency towards hierarchy or tendency towards discrimination. Our tendency to forget the least well off amongst us that those are parts of the human condition that should be warning signs, because weve seen all of those things happen and it hasnt painted a rosy picture.