Measles has no treatments. Getting some may not be easy

A highly effective vaccine has long kept measles at bay in many parts of the world. But as childhood vaccination rates drop, leaving a growing population vulnerable to the extremely contagious virus, one question takes on new urgency: What’s the backup plan?

There are currently no antiviral treatments against measles. Though physicians can offer ways to manage symptoms, which often include fever, fatigue, cough and a hallmark blotchy rash that spreads from head to feet, they can’t fight off the virus itself. 

“We haven’t had the need to develop measles antivirals,” said Ruth Lynfield, an epidemiologist at the Minnesota Department of Health in St. Paul, in a May 27 news briefing. “It hasn’t been a priority. I do think we need to invest in that now.” 

The lack of measles-specific treatments is in part due to the vaccine’s success. With two doses, the shot prevents about 97 percent of measles cases. Vaccination rates above 95 percent across a population create a blockade of protection that the virus has a tough time breaking through. That blockade protects people who can’t get the shot, including babies younger than a year old and people with compromised immune systems.

But vaccination rates are slipping around the globe, including in the United States and Canada, as well as some European countries. The backslide can be attributed in part to concerns about vaccine safety that are not supported by scientific evidence, as well as distrust of medical professionals and lack of access. Funding cuts for global aid could also lead to lower vaccination rates in regions where measles still circulates broadly, which could drive future outbreaks.

As a result, measles cases in the United States are on the rise. This year, cases are poised to surpass last year’s count — the highest since 1991. Of the 2,030 cases reported as of June 4, more than 90 percent have been in unvaccinated people or in people whose vaccination status is unknown. Based on the deluge, which began in January 2025, the country is at risk of losing its measles elimination status.

One of the biggest misunderstandings about measles is that it’s “not that bad,” says Kathryn Hastie, a structural virologist at the La Jolla Institute for Immunology in San Diego. But the virus can cause a range of complications that can severely impact people’s lives, including pneumonia and blindness. The virus can erase immune memory, leaving people vulnerable to other infections. What’s more, about 1 out of every 1,000 people infected with measles develop encephalitis, which can result in permanent brain damage. And 1 to 3 children, a group at high risk of measles, die of the disease for every 1,000 that are infected. 

Antivirals and other treatments could help protect those who are vulnerable, but the research is limited and getting drug candidates to market will be a bumpy road. 

Halting replication

One approach to treating measles it to repurpose drugs that work for other diseases. Already approved drugs with broad antiviral activity could, in theory, be rapidly deployed if proven effective against measles.  

But some researchers hope to find a new drug that could treat measles and its viral cousins. 

Richard Plemper, a virologist and antiviral drug developer at Georgia State University in Atlanta, began using the measles virus as a tool to study how the immune system works in the early 2000s, around the time the United States achieved measles elimination. When measles remained a global problem, he says, “it actually became worthwhile to consider, do we maybe need a measles drug?”

Studies suggested that a chemical probe that the team designed to switch off certain viral functions, including replication, might be turned into an effective treatment. But because of the availability and potency of the measles vaccine, Plemper decided to search for a drug for the entire subfamily of viruses that measles belongs to. The Orthoparamyxovirus subfamily includes Nipah virus and two human parainfluenza viruses, which also lack treatments. 

Like many viral infections, including influenza, these viruses replicate and cause disease quickly. Once a person becomes sick, typically several days after exposure, the window of opportunity for treatment is short. “The paradigm must be the earlier we treat, the better,” Plemper says. The virus may have already stopped replicating by the time a person is severely ill, making antiviral treatment ineffective. 

Plemper and colleagues tested more than 100,000 potential compounds, one of which they developed into the antiviral candidate GHP-88310. The drug has showed promise in ferrets infected with canine distemper virus, an Orthoparamyxovirus that is sometimes used as a proxy for measles in small mammals. Though rodents and ferrets can get infected with the measles virus, they don’t have all the same symptoms that people do.

GHP-88310 dampened viral replication in the ferrets when given daily starting three days after infection, Plemper and colleagues reported May 22 in Science Advances. All treated animals also survived. By binding to a key viral protein, the drug “puts a foot on the brake,” Plemper says.

And the target protein is important for replication across this subfamily of viruses. “This compound is so attractive because it is equally effective against many of the related major human pathogens, of which measles is one,” Plemper says.

The drug still has a long way to go before it could be used in people, but he hopes that it could one day help people who aren’t vaccinated, perhaps even as a prophylactic to prevent measles after an exposure. 

A helping hand for the immune system

Measles-attacking monoclonal antibodies produced in the lab might be another treatment option. 

“You can think of monoclonal antibodies as kind of an on-demand immunity,” Hastie says. Vaccines work by teaching the body how to recognize measles and developing long-term defenses over a few weeks. Monoclonal antibodies — which are widely approved to treat viral infections like RSV and Ebola, as well as some cancers and autoimmune diseases — deliver immune-triggering proteins that get to work immediately. “What we can do with monoclonal antibodies is essentially deliver hand-picked antibodies that are the best of the best to try and control the viral infection at the time of infection, either preexposure or post-exposure,” she says. 

“Vaccines, to some degree, fell victim to their own success.”

Richard Plemper
virologist

Hastie and colleagues recently determined the structures of four measles antibodies from a vaccinated person. Infusing those antibodies into infected cotton rats decreased the amount of measles virus in the rats’ lungs, the team reported May 7 in Cell Host and Microbe. One antibody even reduced the virus to an undetectable level. Because measles is spread through respiratory droplets, the findings hint that treatment might dampen transmission. 

The work follows studies of a different monoclonal antibody candidate called mAb 77, which also diminished the viral load in cotton rats. But that antibody — which is undergoing additional testing in primates — originated from a mouse. Using it in people requires tweaking the immune protein so that the body doesn’t treat it as a foreign invader. The four human antibodies wouldn’t require that step. They next need to be tested in nonhuman primates.

One drawback with monoclonal antibodies is that treatment can be more expensive than an antiviral, Hastie says. Because the antibodies are highly specific for their targets, however, the chance of side effects is low. 

The challenge of clinical trials

There are no clinical trials currently under way for measles treatments, and getting one started could be difficult. One issue is that there need to be enough cases for a meaningful sample size, and in terms of trial logistics, those cases need to be in a predictable timeframe and geographic area.

With measles, “we don’t know exactly where the outbreaks will happen,” Plemper says. Thousands of people get sick with measles every year in some countries — Yemen, Pakistan, Sudan and others — but that’s often because people there don’t have easy access to vaccines. “If you cannot reach the people for vaccination, then you would struggle to enroll them for a clinical trial,” Plemper says. 

There is also the question of who would fund such a trial, since few people might require treatment, though some U.S. biotech companies are taking steps to begin testing monoclonal antibodies. Another is how it could be done ethically. Any unvaccinated children should be offered the vaccine rather than enrolled in a treatment trial.  

Because of these challenges, Plemper and his team are planning to test GHP-88320 on a different, but closely related, virus first: human parainfluenza virus type 3. The common virus, which infects people globally, is an “irritation” most of the time, Plemper says, causing mild, coldlike symptoms. But infections can be life-threatening for transplant patients whose immune systems are suppressed to lower the risk of organ rejection.

The hope is that GHP-88310 will prove helpful against that virus, which doesn’t have a vaccine. And because measles is in the same family of viruses, it could ultimately be available for use during measles outbreaks, too.

“Vaccines, to some degree, fell victim to their own success,” Plemper says. Preventing disease in the first place will always be the best approach, but emerging antivirals and monoclonal antibodies could provide a needed backup, he notes. “Maybe we need this last kick to completely silence the virus.”