COVID-19 Breakthrough Infections More Common, More Severe Among Immunocompromised Individuals


Studies support the use of a COVID-19 vaccine booster dose to increase protection among immunocompromised individuals.

Breakthrough COVID-19 infections in fully vaccinated individuals are considerably more common among immunocompromised individuals, according to a study published in the Journal of Medical Economics. The retrospective cohort study used data from approximately 1.2 million individuals.

“Several countries are currently experiencing a resurgence of SARS-CoV-2 infections despite the rollout of mass vaccination programs,” said Manuela Di Fusco, MSc, lead author from the Pfizer Health Economics and Outcomes Research team, in a press release. “While COVID-19 mRNA vaccines help protect people from getting infected and severely ill, the risk of breakthrough infections in fully vaccinated people is not completely eliminated.”

The investigators found that the overall percentage of fully vaccinated individuals with breakthrough infections between December 10, 2020, and July 8, 2021, was 0.08%. However, though only 18% of the individuals studied were immunocompromised, 38% of breakthrough infections were in immunocompromised individuals, as well as 60% of all hospitalizations and 100% of deaths.

“The results supplement other real-world studies and support the introduction of a third dose of a COVID-19 vaccine to increase protection among the immunocompromised individuals,” Di Fusco said in the release.

Analyzing health care records, investigators found that 17.7% of the individuals reviewed were identified as immunocompromised. These included patients living with advanced HIV/AIDS, cancer, kidney disease, rheumatologic or other inflammatory conditions, other immune conditions, and bone marrow or organ transplant recipients. Out of the total of 978 breakthrough infections, 374 occurred in immunocompromised individuals.

“While the study leveraged a large dataset that has been previously used for healthcare research in the US, the findings should be interpreted in the context of multiple limitations, including coding accuracy and data representativeness beyond the study period,” Di Fusco said in the release. “Our study results advance the understanding of post-vaccination outcomes and support recent recommendations to provide a third primary series dose of an mRNA COVID-19 vaccine to patients with weaker immune systems after the initial two doses.”


Study on over a million people shows breakthrough COVID-19 infections occur more often and are more severe in immunocompromised [news release]. EurekAlert; November 30, 2021. Accessed December 1, 2021.

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