Fully vaccinated people with weaker immune systems contract COVID-19 three times more often and have more severe illness than those with strong immune systems, a study published Nov. 30 in the Journal of Medical Economics found.
The retrospective analysis, led by Pfizer researchers, involved the health records of nearly 1.3 million people aged 16 and older who had received both doses of Pfizer-BioNTech's COVID-19 vaccine from Dec. 10, 2020, to July 8, 2021. Of those, about 18 percent had immunocompromising conditions, such as cancer or kidney disease.
Findings showed the proportion of people with breakthrough infections was three times higher among immunocompromised individuals at 0.18 percent compared to non-immunocompromised people at 0.06 percent.
While breakthrough cases were rare overall, with just 0.08 percent of fully vaccinated people contracting COVID-19, immunocompromised people accounted for more than 38 percent of the infections, despite representing just 18 percent of the study group. About 60 percent of hospitalizations occurred among immunocompromised people, and the two people who died from their illness both had weakened immune systems.
"COVID-19 vaccine breakthrough infections are rare but more common and severe in immunocompromised individuals," researchers said. "The findings from this large study support the FDA authorization and CDC recommendations to offer a third vaccine dose to increase protection among immunocompromised individuals."
Amid growing concern over the emergence of the variant B.1.1.529, known as omicron, the CDC expanded its official COVID-19 vaccine booster recommendations Nov. 29, urging all Americans aged 18 and older to get their booster six months after completing their initial immunization series with the Pfizer-BioNTech or Moderna vaccines, or two months after the Johnson & Johnson shot.