Neil Gupta is an instructor in internal medicine and pediatrics at Harvard Medical School and a clinical director for the nonprofit organization Partners in Health. Paul Farmer is the Kolokotrones university professor at Harvard University, an infectious-disease physician at the Brigham and Women’s Hospital and co-founder of Partners in Health.

Three years ago, we wrote about the wide gap in access to hepatitis C treatment, hoping that mistakes made in the world’s response to AIDS would not be repeated in another epidemic of a lethal, blood-borne disease.

Our worst fears have been realized. The World Health Organization now reports that 4 out of 5 people infected with hepatitis C aren’t even aware of it. Of those who do know, fewer than 1 in 50 have received treatment. These numbers are far worse in parts of South Asia and sub-Saharan Africa, where the majority of the global extreme poor live. In many places, such as Rwanda, infected patients remain on waiting lists for treatment, without which many succumb early to liver failure, cancer and other related complications.

Unfortunately, it bears repeating: This is a failure not of science but of delivery.

Hepatitis C presents the world with an epidemic of massive proportions, one that slowly and silently afflicts more than 70 million people worldwide, more than even HIV. It kills one person every 80 seconds, claiming more lives each year than Ebola, Zika and cholera combined.

Scientific investments have already yielded a new class of medications, called direct-acting antivirals, which, among those with access to them, have transformed hepatitis C from a stubborn and difficult-to-treat chronic infection to one that can be rapidly cured.

A magic bullet for a global epidemic? Not yet. The initial prices for these medications have been up to $1,000 per pill in the United States — or more than $84,000 to cure a patient. As expected, such prices triggered anxiety, and sometimes outrage, among patients and families, health-care providers, i nsurers and governments around the world.

There is cause for optimism in some of the world’s more impoverished settings. Several pharmaceutical companies have allowed, and even encouraged, production and sale of generic drugs in poor countries at a fraction of the price charged in richer ones. The same therapies initially released at prohibitive prices in the United States and Europe can now be purchased for less than $500 in some low-income countries. And in several countries, activism by patients, providers and allies has stalled or denied the granting of patents, which may portend even steeper reductions in prices.

Still, many of the countries in which we work, such as Rwanda, Liberia, Sierra Leone, Malawi and Haiti, continue to lack the staff, stuff, space and systems needed to deliver modern medicine and promote public health. How can patients benefit from a cure if there is no testing available or if financial or geographic barriers prevent them from even reaching a health facility?

This problem, of course, is not unique to hepatitis C. Inadequate or absent health systems have facilitated the explosive spread of cholera, Ebola and drug-resistant tuberculosis.

This offers yet another opportunity to learn from the global response to AIDS. Two decades ago, public-health experts and policymakers debated the “cost” and “value” of treating people dying of AIDS in the poorest pockets of the world. Can we test enough patients? Are there staff to deliver medications and monitor side effects and outcomes? Will patients be willing to take them?

Amid these delays, more than 30 million people needlessly lost their lives to a treatable illness. But a massive global AIDS movement soon committed billions of dollars to reining in this scourge. In some places, these investments were leveraged to build facilities, stock shelves and train staff to deliver HIV medications. More than 18 million people with HIV — most of them living in poverty — are now receiving antiretroviral therapy. When patients are receiving effective therapy, they’re less able to transmit the virus to others. AIDS treatment has proved to be one of our most effective means of AIDS prevention.

Despite these accomplishments, far more needs to be done to build and rehabilitate broken — or nonexistent — health systems. Without them, we’re poorly equipped to fight other diseases, such as hepatitis C.

Efforts are underway in several low- and middle-income countries, such as Egypt, Georgia, Indonesia and Rwanda, to test and treat neglected populations for hepatitis C and simplify care delivery. Such work is at the cutting edge of broadening global access to the now-available therapeutics. But it’s only the first step.

Friday, as we mark World Hepatitis Day, let’s commit to learning from the past and to delivering on the promise of science and medicine to the benefit of those in need of them both.