Every vaccinated participant who endured serious COVID-19 outcomes as part of a new study of more than 1 million people had at least one risk factor that left them vulnerable, according to the Centers for Disease Control and Prevention (CDC).
The CDC research published Thursday provided further evidence that the COVID-19 vaccines protect recipients, making severe outcomes "rare." Just 189 people experienced these outcomes out of more than 1.2 million who got their primary vaccination series between December 2020 and October 2021.
All of these patients who endured serious outcomes, such as intensive care unit admission and death, had one or more risk factors that made them more likely to develop serious illness from the virus.
The risk factors included being aged 65 and older, being immunocompromised, or having underlying conditions involving pulmonary disease, liver disease, chronic kidney disease, neurologic disease, diabetes or cardiac disease.
The study defined serious COVID-19 outcomes as hospitalization with diagnosis of acute respiratory failure, need for noninvasive ventilation or ICU admission and death.
Just 36 people in the study died of COVID-19 after getting their primary vaccination series, with 78 percent of them having at least four risk factors. In total, 2,246 vaccinated people in the study contracted COVID-19, and almost 77 percent had at least one risk factor.
The research suggests people vaccinated with the primary series who are older, immunocompromised or have certain underlying conditions are more likely to develop breakthrough cases, supporting increased precautions and boosters among more vulnerable populations.
Out of the 3,395 people in the study who received booster or additional dose, only 27 contracted COVID-19, with three having severe outcomes. None were admitted to the ICU or died.
Data collection for the study ended in October, before the highly transmissible omicron variant was detected in the U.S.
A majority of the study participants - almost 73 percent - had been vaccinated with Pfizer-BioNTech's shots, while 20 percent had Moderna and 6.5 percent had Johnson & Johnson.
CDC data shows almost three-quarters of the U.S. adult population and nearly 88 percent of those aged 65 and older are considered fully vaccinated. A total of 38 percent of adults and almost 60 percent of older Americans have received a booster shot.