How well does a new Alzheimer's drug work for those most at risk?

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A new drug for Alzheimer's disease, called lecanemab, got a lot of attention earlier this year for getting fast-tracked approval based on a clinical trial that included nearly 1,800 people.

While some saw it as undeniable progress for a disease with no other proven treatment, others urged caution because of severe side effects and the finding of only a "modest" effect. Dr. Jonathan Jackson, Assistant Professor of Neurology at Harvard Medical School, has another concern: the racial and ethnic makeup of the trial.

The clinical trial for lecanemab was the most diverse for an Alzheimer's treatment to date, but it still was not enough to definitively say if the drug is effective for Black people.

"[In] the world's most diverse Alzheimer's trial, a giant trial of 1,800 people that lasted for a much longer time than most trials did, we're still not sure that all of the groups that are at highest risk of Alzheimer's disease actually see any kind of benefit," Jackson, director of the Community Access, Recruitment, and Engagement Research Center, says.

The makers of lecanemab say the trial was able to enroll more Black and Hispanic patients by removing some of the requirements that had been in place for previous trials. They cite tapping into community outreach groups and making it "easy for the patients to enroll into the study, and we made it easy for the patients to actually continue to participate in the study," says Shobha Dhadda, Vice President of Biostatistics and clinical development operations for Neurology at the pharmaceutical company Esai.

The trial enrollment comes close to reaching the racial breakdown of people 65 and older according to the census, but Jackson says that's the wrong goal. Black and Hispanic people, women, and those with a genetic predisposition are all at disproportionately high risk for developing Alzheimer's. Jackson says companies should be overrepresenting these groups in their trials.

"If we continue to study privileged populations ... we're leaving huge questions unanswered about how Alzheimer's works, how it progresses, and what are the significant risk factors," he says. "So when you're designing a study, you should really worry less about the census and more about trying to represent those who are disproportionately affected."

On today's episode, Jonathan and Short Wave co-host Emily Kwong delve into how drug developers can overlook those hardest hit by the disease they're trying to treat.

Have suggestions for what we should cover in future episodes? Email us at shortwave@npr.org.

This episode was produced by Liz Metzger and edited by Gabriel Spitzer. Anil Oza contributed additional reporting and checked the facts. Patrick Murray was the audio engineer.