Although he was fully vaccinated, former secretary of state Colin Powell succumbed to COVID-19 complications. The four-star general was 84 when he died Monday morning.

Powell served in several Republican administrations and helped shape American foreign policy in the last years of the 20^th century and the early years of the 21^st, said CNN.

“We have lost a remarkable and loving husband, father, grandfather, and a great American,” his family said in statement posted on Facebook.

According to CNBC, Powell was at high-risk for breakthrough infection from COVID-19 despite the vaccine. He was elderly and suffered from multiple myeloma, a blood cancer that studies have shown make the shots less effective.

People with weakened immune systems from conditions such as cancer or HIV, or from undergoing an organ transplant, account for just 2.7% of the American population, but make up 44% of hospitalized COVID-19 breakthrough cases, says the Centers for Disease Control and Prevention.

A study published in July found that only 45% of patients who had active multiple myeloma had an adequate immune response after being vaccinated by either the Pfizer or the Moderna mRNA vaccines. Only 22% had a “partial” response, says CNBC.

“The goal of the vaccine is to dramatically reduce your chance of suffering or being hospitalized or dying but it doesn’t eliminate it,” said Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia and a leading government advisor on vaccines.

People with multiple myeloma have difficulty fighting off infections, which is the same mechanism that prevents them from achieving full immunity from the vaccines. The Food and Drug Administration authorized booster shots for this population last August, but it is not clear if Powell received his third shot.

Offit said that vaccinated people with weak or compromised immune systems should continue wearing masks and social distancing, according to CNBC.