COVID-19 Vaccination Protects Against Severe Clinical Outcomes in Hospitalized Adults


Overall, 91.5% of the hospitalized adults with COVID-19 were unvaccinated and 8.5% of patients were fully vaccinated.

clinician wearing face mask and gloves holds bottle for injection of covid-19 vaccine with syringe

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For hospitalized adults with COVID-19 infection, having received a COVID-19 vaccine significantly reduced the risk of severe illness or death compared with not having received an immunization. COVID-19 vaccine protection against severe outcomes was comparable between the Pfizer-BioNTech and Moderna mRNA-1273 vaccines.

Investigators shared these results from a population-based propensity score-matched study in a poster at IDWeek 2022, held October 19-23, 2022, in Washington, DC. Their goal was to evaluate the impact of COVID-19 vaccination on rates of intensive care unit (ICU) admission and death among hospitalized adult patients with confirmed SARS-CoV-2 infection. Overall, 91.5% of the hospitalized adults with COVID-19 were unvaccinated and 8.5% of patients were fully vaccinated.

The retrospective study was performed using data collected from the Memorial Healthcare System (MHS) in Hollywood, Florida, between June 1 and September 21, 2021, which coincided with the spike in cases caused by the B.1.617.2 (Delta) strain. Participants were divided into 2 groups: vaccinated and unvaccinated, with vaccinated defined as individuals who received 2 doses prescribed by the vaccination protocol with ≥ 14 days administration of the second dose of vaccine before illness onset. For the study’s purposes, unvaccinated was defined as individuals who had no record of vaccination against COVID-19 or partially vaccinated individuals with a single dose vaccination or <14 day after the second dose administration before illness onset>< 14 days after the second dose administration before illness onset.

Investigators matched vaccinated and unvaccinated patients 1:1 and used standardized mean differences with a maximum propensity score probability difference of 10% to evaluate the balance of baseline characteristics between the 2 groups.

A total of 3810 adults were hospitalized with COVID-19 at MHS during the study period. After excluding duplicated cases, deaths, or cases with missing data, 3351 patients were included in the pre-matched cohort (vaccinated n = 284; unvaccinated n = 3067). After propensity score matching 1:1, 524 patients were matched (vaccinated n = 262; unvaccinated n = 262). Thirty-seven received the Moderna vaccine and 225 received the Pfizer-BioNTech vaccine.

Overall, breakthrough COVID-19 infections among the fully vaccinated were much more common in older patients (67% were > 65 years old, 19% were between 55–64 years old, and 14% were < 55 years).

In the group of unvaccinated patients with COVID-19, 29% were > 65 years old, 20% were between 55–64 years old, and 51% were < 55 years.

“Patients with vaccine breakthrough COVID-19 infection had a significantly higher comorbidity profile compared with unvaccinated, including hypertension (85.6% vs. 51.9%), diabetes (45.6% vs. 31.8%), chronic obstructive pulmonary disease (22.2% vs. 5.7%), chronic kidney disease (30.6% vs. 12.4%), ischemic heart disease (36.6% vs. 11.3%), cerebrovascular disease (17.6% vs. 4.8%), malignancy (17.1% vs. 4.4%) and smoking (44.7% vs. 21.1%) (P < .0001),” investigators reported.

Vaccination provides protection against severe clinical outcomes, including severe illness and death compared with no vaccination, the research team concluded.

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