(CNN) Gen. Colin Powell died Monday from complications of Covid-19, and experts say his death shows how important it is for more people to get vaccinated and stop the spread of the virus.
Powell was fully vaccinated, but a source close to the matter confirmed to CNN he had multiple myeloma, a type of blood cancer that would have affected his immune response to the vaccine, and made it difficult to fight the virus.
Peggy Cifrino, Powell's chief of staff, said Powell, 84, also had Parkinson's disease, a neurodegenerative disorder.
Multiple myeloma is among the most common blood cancers in the United States, and it disproportionately affects Black Americans. They have nearly twice the risk of developing the disease as White Americans.
Although the Covid-19 vaccines provide strong protection against severe disease and death in healthy people, multiple myeloma patients are among the immunocompromised groups who may not respond as well, studies have shown. One study published in Nature in July showed that only 45% of multiple myeloma patients developed an adequate response to the vaccine, while 22% had a partial response. One-third had no response.
Dr. Jonathan Reiner, a CNN medical analyst and professor of medicine and surgery at George Washington University, said Monday that Powell "represented our most vulnerable population in this country."
"He was over the age of 80, he had cancer, and a treatment for his cancer made him vulnerable," Reiner told CNN's Jim Sciutto and Erica Hill. "So, when we try and convince young people who feel that they are low-risk from the virus itself why they need to be vaccinated, it's to protect our treasures, our people like General Powell, our grandparents, because while, you know, a 25-year-old may do quite well with the infection, if they spread it to someone like General Powell, they will not. That is the imperative for vaccination in this country."
Multiple myeloma is a cancer that forms in white blood cells called plasma cells.
When plasma cells are healthy, they help the body fight off infections and toxins by making immune system proteins called antibodies.
Any kind of cancer begins when cells grow out of control. With this type of cancer, the cancerous plasma cells start to accumulate.
"When you have multiple myeloma, the cancer cells fill up the bone marrow and crowd out all of the cells that are making the immune system, so your immune system becomes tremendously weakened," said Dr. Drew Pardoll, Abeloff professor of oncology, medicine, pathology and molecular biology and genetics at the Johns Hopkins University School of Medicine.
Powell's cancer made it difficult to fight off coronavirus infection, and treatment could have further weakened his immune system.
Treatment for multiple myeloma can include chemotherapy and steroids. Both can weaken the immune system.
A stem cell transplant may also be part of treatment for some patients, according to the American Cancer Society.
Earlier this year, the US Food and Drug Administration approved a type of treatment called chimeric antigen receptors T-cell therapy, or CAR-T therapy, for people with multiple myeloma who had not responded to earlier cancer treatments. Such therapies change a patient's T cells so they can better attack cancer cells.
"We've made good progress, but it's still a tough disease to treat," said Dr. William Cance, chief medical and scientific officer for the American Cancer Society.
Multiple myeloma patients can live for many years with treatment, but it's not considered curable.
"There are many treatments for multiple myeloma that oftentimes will work early on, but ultimately, the tumor cells develop a resistance, and you'll go to another therapy, and another therapy," Pardoll said. "There is essentially no therapy for multiple myeloma that cures the patient of the disease. So oftentimes, with the therapies available, individuals can live for many years, sometimes even over 10 years."
Even if vaccinated, people with multiple myeloma -- or many other health conditions -- may not be able to mount the kind of immune response a healthy person would.
"Vaccines like the Covid vaccine give our immune systems a little tiny taste or a tiny example of the Covid virus so that they produce these antibodies that put a lot of extra soldiers on guard who also specifically can attack that virus," Cance said. "When the plasma cells that make antibodies become cancerous, they are not as adept at making the antibodies that you need for specific pathogens like the virus that causes Covid."
Studies have shown that patients with blood cancers, including multiple myeloma, had a higher risk of severe Covid-19, said Dr. Anthoni Ribas, director of the Tumor Immunology Program at the UCLA Jonsson Comprehensive Cancer Center and president of the American Association for Cancer Research, who has been working on this research.
Among patients with common blood cancers, only 40% to 70% produce antibodies to fight Covid-19 after vaccination, compared with 98% to 100% of healthy people, he said.
For patients with multiple myeloma it may be even fewer.
"These patients are at a disadvantage to fight the virus. Even with the vaccine, the data that we have shows that people with multiple myeloma, 20% to 30% of them do not have a good immune response to the vaccines," said Ribas.
Starting in August, patients with blood cancers were among the immunocompromised people eligible for a third dose of the Pfizer and Moderna Covid-19 vaccines. That additional dose was expected to help some mount a stronger immune response.
More adults are already eligible to receive boosters of the Pfizer Covid-19 vaccine, and the US Food and Drug Administration is considering boosters for the Moderna and Johnson & Johnson vaccine recipients, as well.
Cifrino, Powell's longtime chief of staff, told CNN that Powell had received the two-dose Pfizer vaccine, and received a second shot in February. He had been scheduled to get a booster last week, but did not receive it because he was ill.
"This is not a failure of the vaccine, but rather a failure of the person's body in whom the vaccine was administered," said Dr. David Cohn, the chief medical officer at the Ohio State University Comprehensive Cancer Center.
It's essential that people around those with multiple myeloma -- or other immunocompromising conditions -- get vaccinated.
"It's not their fault that they can't generate a good immune response, so the key thing is to have everybody else around them fully vaccinated," Ribas said, noting that current guidelines do not recommend boosters for the caretakers of people who have a low response to the vaccine. He hopes those guidelines will change.
"We need to be able to get everyone around them well protected so they do not carry the virus to them," he said.