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Older people may be at higher risk for hospitalization from breakthrough COVID

NEW YORK 23/09 - Older people vaccinated against COVID-19 may be more likely than younger individuals to develop severe breakthrough disease and need hospitalization.

That's according to new research from Yale New Haven Health System, in Connecticut, where nearly one in five patients admitted with confirmed COVID-19 had received at least one dose of a COVID-19 vaccine.

The findings were published in The Lancet Infectious Diseases.

In an email to Reuters Health, corresponding author Dr. Hyung J. Chun of Yale Cardiovascular Research Center noted that the study took place before the Delta variant of SARS-CoV-2 became predominant in the United States.

At that time, he added, breakthrough cases were a lower percentage of hospitalized COVID-19 cases than they are now. "This would be expected based on the emergence of the Delta variant, as well as longer period of time that has elapsed since vaccination."

Despite these differences, Dr. Chun said, the more-vulnerable population of older individuals "appears to be similar between our study and what is being reported recently by the CDC, where 70% of hospitalized cases are people over age 65, and 87% of deaths are also in this age group."

Of the 969 patients admitted to Yale New Haven Health System with a confirmed positive PCR test for SARS-CoV-2 between March 23 and July 1 of this year, 172 (18%) had received at least one dose of a COVID-19 vaccine, Dr. Chun and colleagues found.

Of these patients, 103 had received a partial vaccine course (one dose of the Pfizer-BioNTech or Moderna vaccine), 15 had received a complete course (two doses of those vaccines or one of the Janssen vaccine within 14 days before symptom onset or a positive PCR test), and 54 were fully vaccinated at least 14 days before symptom onset or a positive PCR test.

These 54 patients were deemed to have breakthrough infections.

Among them, 25 (46%) were asymptomatic (hospitalized for reasons other than COVID infection), four (7%) had mild disease, 11 (20%) had moderate disease, and 14 (26%) had severe or critical illness.

The median age in the latter group was 80 years. Four of the 14 patients required intensive care, one required mechanical ventilation and three died.

Pre-existing comorbidities in the group with severe COVID-19 included cardiovascular disease (12 patients), overweight (nine patients), lung disease (seven), type-2 diabetes (seven), malignancy (four), and use of an immunosuppressive agent (four).

The authors say an ineffective immune response mounted against vaccines in patients with comorbidities could be one reason that more than one-quarter of breakthrough infections resulted in severe or critical illness.

The report also highlights "a higher number of patients with severe or critical illness" in those who received the Pfizer-BioNTech vaccine than in those who received either of the other two vaccines, a finding the authors say calls for further investigation.

Dr. Francesca Torriani of the Division of Infectious Diseases and Global Public Health at the University of California, San Diego, compared the Yale study with one on breakthrough SARS-CoV-2 infections in healthcare workers, which she and colleagues published earlier this year (

"The very important difference" between the studies, she explained, is that the California study evaluated breakthrough patients in "a young and healthy workforce" whose median age was just 39.

Still, there are similarities, said Dr. Torriani, who was not involved in the new research. The California study found a fifth to a quarter of COVID hospitalizations to have resulted from breakthrough infections. In addition, all of the few cases that required intensive care had severe comorbidities, such as solid organ or bone-marrow transplant, or were at high risk of severe disease, for example because of obesity.

"This is an important point of discussion that I hope will be discussed in the next Food and Drug Administration and Advisory Committee on Immunization Practices meetings on who should receive boosters," Dr. Torriani concluded.

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