Kaiser Permanente study finds higher risk if unvaccinated, lacking booster, or having certain health conditions
By Jan Greene
A large analysis of COVID-19 patients in Northern California confirms the value of vaccination, finding higher rates of hospitalization and advanced medical care for COVID-19 patients who were unvaccinated, were vaccinated but not boosted, or who had an additional health condition such as obesity or heart disease.
The study, published June 16 in The Lancet Regional Health – Americas, examined records for 118,078 patients of Kaiser Permanente Northern California who had a positive COVID-19 test and examined their medical progress for the following 3 weeks.
The results confirm the value of receiving the complete recommended series of COVID-19 vaccinations, said study lead author Jacek Skarbinski, MD, research scientist with the Kaiser Permanente Division of Research and infectious disease specialist with The Permanente Medical Group. “COVID-19 vaccines and boosters remain the most important tool that we have to prevent severe illness with COVID-19,” he said.
The study found significant differences between the patients who experienced a COVID-19 infection during the period when the delta variant was dominant compared with the omicron period. Those infected during delta had higher hospitalization rates (7.8% vs 2.4%), hospitalizations requiring low-flow oxygen support (6.4% vs 1.6%) or mechanical ventilation (0.7% vs. 0.1%), and death (0.7% vs 0.2%).
Vaccination played a major role in risk of severe health outcomes: unvaccinated patients were 8 times more likely to be hospitalized than patients who completed the initial vaccination series plus a booster. Patients who had only the initial vaccination series were 70% more likely to be hospitalized than those who had the initial series plus a booster.
Having an additional health risk factor (known as a comorbidity) also increased risk of severe outcomes. These included older age, obesity, diabetes, and atherosclerotic cardiovascular disease (blocked arteries).
One purpose of the analysis was to learn whether risk factors might change with the omicron period and they did not, explained senior author Lawrence Kushi, ScD, research scientist with the Division of Research. “Even though rates of infection were higher for the omicron variant than the delta variant, rates of poorer outcomes such as hospitalization and death were lower for omicron, and risk factors were largely the same.”
Knowing the current risk factors for severe COVID-19 disease is important for clinicians who are managing limited supplies of medications and other therapies, said Skarbinski, who practices at Kaiser Permanente Oakland Medical Center and treats COVID-19 patients. “Understanding the risk factors for severe COVID-19 is critical to ensure that we deliver outpatient therapies such as oral antivirals or SARS-CoV-2 monoclonal antibodies to those who are most likely to benefit,” he said.
The study also highlighted omicron’s impact on hospital resources: while the risk of severe medical outcomes with omicron for an individual was lower than with delta, omicron infected more people and so increased the total number of people hospitalized with it. That has placed a strain on hospitals and intensive care units that continues, the authors said.
The study was funded by the National Cancer Institute and The Permanente Medical Group’s Delivery Science and Applied Research program.
Additional co-authors were Douglas Corley, MD, PhD, Charles Quesenberry, PhD, Mariah S. Wood, MPH, Tyler C. Chervo, MPH, Eric P. Elkin, MPH, Emily Vance, MPH, Laura B. Amsden, MSW, MPH, and Crystal Hsiao, MPH, all of the Division of Research.
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About the Kaiser Permanente Division of Research
The Kaiser Permanente Division of Research conducts, publishes and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and society at large. It seeks to understand the determinants of illness and well-being, and to improve the quality and cost-effectiveness of health care. Currently, DOR’s 600-plus staff is working on more than 450 epidemiological and health services research projects. For more information, visit divisionofresearch.kaiserpermanente.org or follow us @KPDOR.