WASHINGTON - Former US Secretary of State Colin Powell died at 84 of COVID-19 complications on Monday, triggering heated debate over the effectiveness of vaccines in the United States.

"General Colin L. Powell, former US Secretary of State and Chairman of the Joint Chiefs of Staff, passed away this morning due to complications from COVID-19," the Powell family wrote in a Facebook post on Monday, noting Powell had been fully vaccinated. He was suffering from serious underlying conditions.

Powell's passing added fuel to those who oppose vaccines in the country, but health experts stressed Powell's death was an exception to the vaccines' protection, not proof they do not work.

"While Powell was fully vaccinated, he also had multiple myeloma, a cancer that suppresses the body's immune response," said Gwen Nichols, chief medical officer at the US Leukemia & Lymphoma Society.

"Multiple myeloma is not curable, so while he may or may not have been on active treatment, his disease, and his age, made him more vulnerable to breakthrough infection, complications and death," she explained.

Powell battled other heightened risks of severe COVID-19.

Besides multiple myeloma, Powell reportedly had surgery for prostate cancer when he was US secretary of state and, more recently, Parkinson's disease.

Neurologic conditions are among those cited by the US Centers for Disease Control and Prevention (CDC) as potentially increasing the risk of severe COVID-19 in patients.

"I'm afraid people will say the vaccine didn't help him," said Robert Murphy, executive director of the Institute for Global Health at Northwestern University Feinberg School of Medicine.

"But the mortality rate for vaccinated people is 11 times less than unvaccinated. People still die from the disease, especially if you are 84 and have underlying health risks. He is one of the unfortunate ones, but he was very high risk," Murphy was quoted by USA Today as saying.

Experts stressed that Powell's passing does not demonstrate the futility of vaccines, but instead underscores the importance of everyone getting vaccinated to protect society's most vulnerable.

A new CDC study published on Tuesday shows that among hospitalized US patients aged 12 to 18 years, vaccine effectiveness of two doses of Pfizer-BioNTech vaccine against COVID-19 hospitalization during June to September was 93 percent.

Unvaccinated people have an 11 times higher risk of dying from COVID-19 than fully vaccinated people, according to another CDC study published recently.

In addition, the study shows that unvaccinated people have a six times higher chance of testing positive for COVID-19 than fully vaccinated people do.

"Former Secretary of State Colin Powell's death from COVID-19 complications signifies the latest wake-up call in the United States's extended battle against the virus, demonstrating the continued risk the pandemic poses to American lives," said a report of The Hill.