People with Down syndrome are the most likely of all vaccinated adults to die from COVID-19, new research suggests.

Those with the chromosomal disorder have a 12-fold increased risk of death if they contract the coronavirus after receiving at least one vaccine dose, according to findings published in the British Medical Journal this month. That’s a higher risk than any other group.

The study looked at medical records for 6.9 million vaccinated adults in the United Kingdom, 5.2 million of whom received two vaccine doses. There were 2,031 deaths from COVID-19 and 1,929 hospital admissions related to the virus in those studied. Only 81 of the deaths and 71 of the hospitalizations occurred at least 14 days after the second vaccine dose.

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Researchers used a tool they developed called QCovid to establish cumulative risk scores for hospitalization or death from COVID-19 for different groups. The tool factors for age, sex, ethnic group and the rate of COVID-19 infections.

In addition to people with chronic disorders like Down syndrome, other groups with elevated odds for hospitalization and death after vaccination include those who are immunosuppressed as a result of chemotherapy, a recent bone marrow or solid organ transplant, the study found. Individuals with HIV/AIDS, those living in congregate settings and people with neurological disorders, including dementia and Parkinson’s disease, are also in the highest risk group.

Overall, there were very few hospitalizations or deaths in people studied who were at least 14 days past their second vaccine dose. Accordingly, the researchers said they do not have enough data to say definitively whether the trends identified in the study will persist.

Nonetheless, the data offers guidance on who is likely to face the most risk following vaccination, they said.

“This enormous national study of over 5 million people vaccinated with two doses across the U.K. has found that a small minority of people remain at risk of COVID-19 hospitalization and death,” said Aziz Sheikh of The University of Edinburgh who worked on the study.

Sheikh said the findings could help identify people who might benefit most from interventions like vaccine boosters and monoclonal antibodies, a treatment that can help prevent the most severe disease progression.

In addition, Julia Hippisley-Cox of the University of Oxford, who led the study, noted that the findings might also help people better assess their own situation.

“Individual risk will always depend on individual choices as well as the current prevalence of the disease, however we hope that this new tool will help shared decision-making and more personalized risk assessment,” she said.