While COVID-19 breakthrough infections—cases after vaccination—are rare, fully vaccinated people with compromised immune systems have them three times more often than those with strong immune systems and have more severe illnesses, according to a real-world US study involving nearly 1.3 million people.In the retrospective study, published today in the Journal of Medical Economics, a team led by researchers from Pfizer analyzed the health records of 1,277,747 people aged 16 or older who had received two doses of the Pfizer/BioNTech COVID-19 vaccine from Dec 10, 2020, to Jul 8, 2021.
The latter part of the study period included the emergence of the Delta (B1617.2) variant in the United States.Rare but severe infectionsOf all people studied,