What Scientists Know About the Risk of Breakthrough Deaths

The death of former Secretary of State Colin L. Powell on Monday from complications of Covid-19 has provided fuel for vaccine skeptics and opponents, who immediately seized on the news that Mr. Powell had been vaccinated to stoke doubts about the effectiveness of the vaccines. But Mr. Powell’s immune system had most likely been weakened by multiple myeloma, a cancer of white blood cells. Both the disease and the treatment can make people more susceptible to infections. His age, 84, may also have increased his risk, scientists said. Mr. Powell received his second dose of the Pfizer-BioNTech vaccine in February, said Peggy Cifrino, his longtime aide. He had been scheduled for a booster last week but fell ill before he received it, she said.