Unvaccinated 10 Times More Likely to Be Hospitalized for Omicron

Will Pass

September 12, 2022

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Unvaccinated people may be 10 times more likely than fully vaccinated people to be hospitalized for the Omicron variant of COVID-19, suggests a large study conducted by the U.S. Centers for Disease Control and Prevention.

The data, which included almost 200,000 COVID-19–associated hospitalizations across 13 states, also showed that vaccinated, hospitalized patients were more often older and already dealing with other health conditions, compared with unvaccinated, hospitalized patients, reported lead author Fiona P. Havers, MD, of the CDC, Atlanta.

"Unlike previously published reports and web pages … this study reports hospitalization rates by vaccination status and clinical and demographic characteristics of hospitalized patients, beginning with the period when vaccines first became available, and includes comparisons of unvaccinated persons, persons vaccinated with a primary series without a booster dose, and those vaccinated with a primary series and at least 1 booster dose," the investigators wrote in JAMA Internal Medicine.

In total, the investigators reviewed 192,509 hospitalizations involving patients 18 years and older. The study period spanned from Jan. 1, 2021, to April 30, 2022. Data were reported month by month, showing that the relative monthly hospitalization rate peaked in May 2021, when it was 17.7 times higher for unvaccinated versus vaccinated individuals (with or without a booster).

To account for differences in clinical course between Delta and Omicron, the investigators also analyzed data sorted into two time periods: July-December 2021 (Delta predominant) and January-April 2022 (Omicron BA.1 predominant). These analyses revealed the greater hospitalization risk presented by Delta. Specifically, unvaccinated people were 12.2 times more likely to be hospitalized for Delta than vaccinated people, with or without a booster, versus 6.8 times for Omicron BA.1.

Study Shows Power of the Booster

A closer look at the Omicron BA.1 data showed the power of a booster dose. From January to April 2022, individuals who were fully vaccinated with a booster dose were 10.5 times less likely than unvaccinated individuals to be hospitalized for Omicron BA.1. Plus, boosted people were 2.5 times less likely to be hospitalized for Omicron BA.1 than people who got vaccinated but skipped the booster.

"The high hospitalization rates in unvaccinated compared with vaccinated persons with and without a booster dose underscores the importance of COVID-19 vaccinations in preventing hospitalizations and suggests that increasing vaccination coverage, including booster dose coverage, can prevent hospitalizations, serious illness, and death," the investigators wrote.

The study also revealed that vaccinated hospitalized patients were significantly older, on average, than unvaccinated hospitalized patients (median, 70 vs. 58 years; P < .001). They were also significantly more likely to have three or more underlying medical conditions (77.8% vs. 51.6%; P < .001)

"A greater proportion of hospitalized cases among vaccinated persons occurred in individuals with medical fragility who were older, more likely to reside in long-term care facilities, and have three or more underlying medical conditions, including immunosuppressive conditions," the investigators wrote.

New Variants Outpacing Data, Vaccines Remain Essential

While data from April 2022 alone showed a 3.5-fold higher rate of hospitalization among unvaccinated versus vaccinated individuals with or without a booster, newer data suggest that emerging strains of Omicron are putting more people in the hospital.

A recent report by the CDC showed weekly hospitalization rates climbing from March 20 to May 31, 2022, which coincided with predominance of the newer Omicron BA.2 variant. While unvaccinated people were still around 3.5 times more likely to be hospitalized than vaccinated people, overall hospitalization rates jumped 3-fold for people 65 years and older, and 1.7-fold for adults younger than 65. Adding further complexity to this constantly evolving situation is that Omicron BA.2 has since been joined by the BA.4 and BA.5 lineages, for which vaccines are now available.

In the paper published in JAMA Internal Medicine, the CDC report, and in a comment for this article, the CDC offered the same take-home message: Get vaccinated.

"These findings reinforce previous research illustrating how vaccination provides protection from hospitalization due to COVID-19," a CDC spokesperson said. "COVID-19 vaccines are proven to help prevent serious COVID-19 illness, and everyone ages 6 months and older should stay up to date with COVID-19 vaccines."

The study published in JAMA Internal Medicine was supported by the CDC. The investigators disclosed additional relationships with Sanofi, GSK, MedImmune, and others.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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