How can treating one patient help another?

New treatments for Hepatitis C give a surprising example of how treating one patient can benefit others

It used to be that patients with a chronic hepatitis C virus (HCV) infection didn’t have great treatment options to prevent the virus from doing persistent damage to their livers. It was hard to get rid of the virus, which causes inflammation in the liver (“hepat-”=liver, “-itis” = inflammation). This inflammation placed patients at risk for liver cancer, scarring and dysfunction of the liver (called cirrhosis), and complete liver failure requiring liver transplantation. As of 2013, about 38% of liver transplants performed in the U.S. were for HCV positive patients (2,433 out of 6,455 liver transplants that year).

That same year, however, new treatments for HCV started to receive FDA approval. These “direct acting antivirals” (e.g., Harvoni) were remarkably effective at treating HCV, to the point that the majority of patients with HCV infection could be cured. Once cured of HCV infections, patients could be spared from further damage from the virus—particularly those who were treated early in the disease process.

Clearly these new drugs would be great for people with HCV infection—and they have been. And if these patients were cured of HCV and no longer progressing toward liver failure, many fewer patients should be needing liver transplants, right?

Ripple effects of treating HCV

In an economic simulation study from 2016, Bapu and others wanted to estimate what the impact of having fewer chronic HCV infections might be on liver transplantation—not just for patients with HCV, but any patient needing a liver transplant.

Donor livers are a scarce resource—patients can wait a long time for liver transplant, and sadly, many die while waiting. But if fewer people with HCV were needing liver transplants because the virus was being treated, the livers that would have been transplanted into patients with HCV could now be transplanted into other patients. (Such ripple or spillover effects of the new HCV drugs that impact patients other than those with HCV are what economists call “externalities.”)

After gathering information on the epidemiology of HCV, the ways in which the infection leads to progressive liver disease, and trends in liver transplantation for people with liver disease of all kinds (not just HCV infection), they created a simulation model to predict what might happen if we systematically screened people for HCV infection and treated any infections with the new drugs.

The model predicted that over the 20-year period from 2015 to 2035, screening and treating for HCV would help 10,490 patients avoid liver transplant. Of course, those livers could then go to 10,490 other patients, saving their lives. The model estimated those livers would go to 7,321 patients who needed transplants for liver disease other than HCV, as well as to 3,169 patients with HCV who were unable to be cured and who otherwise wouldn’t have been transplanted. According to the model, the lives saved by treatment of HCV and subsequent re-allocation of donor livers would translate into billions of dollars in economic value.

Were the predictions right?

Of course, it’s too soon to tell if the model’s predictions out to 2035 were correct. Many people are being screened and treated for HCV, and the available data is encouraging.

One simple statistic suggests that indeed, treatment of HCV is freeing up donor livers for patients with other diseases: in 2022, patients with chronic HCV infection represented only 11% of liver transplants (1,029 of 9,528)—down from the 38% in 2013 when the new HCV drugs were approved.

Beyond this simple figure, a new working paper by economists Kevin Callison, Michael Darden, and Keith Teltser has taken a new, rigorous look at data from 2014 to 2019 to understand how these new drugs for HCV have impacted liver transplants after their first 5 years of broad use. There were a number of encouraging findings:

• Waiting lists for liver transplants were being occupied by fewer HCV-positive patients and more HCV-negative patients; this shift can be explained by an estimated 45% reduction in the addition of new HCV-positive patients to waiting lists

• Patients on the waiting list were healthier, likely because waiting times for livers have decreased with less demand from HCV-positive patients

• Compared to what would have been expected without the introduction of new HCV treatments, the researchers estimated a 39% decrease in transplants to HCV-positive patients coupled with a 36% increase in transplants to HCV-negative patients.

• Over the five year period, researchers estimated 5,682 livers were transplanted to HCV-negative patients as a result of the new HCV drugs, corresponding to an economic value of $7.5 billion

Organ donation and transplantation are one of the most complex aspects of modern medical care, and it would be easy to miss more distant impacts of the new HCV treatments. For example, an increase in transplantation from HCV-positive donors—since new medications for HCV now make it possible to transplant their organs—can increase transplantation and reduce waiting times for other organs like kidneys.

This is just one example of how helping one patient can also indirectly help another. It’s not hard to think of other examples where this might also be the case—stopping the spread of other infectious diseases comes to mind. It can be difficult to think of all the possible ripple effects—all the externalities—of any given intervention, making it challenging to estimate its broad impact, good or bad. But it’s important that we try, lest we miss out on a great opportunity for public health.