Top 5 Takeaways

1. Higher Risk for Unvaccinated: Unvaccinated individuals had significantly higher COVID-19 incidence and hospitalization rates compared to vaccinated individuals, especially those with a booster.
2. Omicron Impact: During Omicron predominance, unvaccinated persons had 3.6 times the infection rate and 23.0 times the hospitalization rate of fully vaccinated persons with a booster.
3. Vaccine Effectiveness: COVID-19 vaccines, particularly with a booster, provided strong protection against severe outcomes during both Delta and Omicron variant predominance.
4. Health Care Strain: The high volume of Omicron infections led to substantial hospitalizations, exacerbating health care system strain, particularly among unvaccinated individuals.
5. Public Health Implications: Staying up to date with COVID-19 vaccinations, including boosters, is critical for reducing infection and hospitalization rates.

Original Article Author and Citation

Corresponding Author

Sharon Balter, sbalter@ph.lacounty.gov

Suggested Citation

Danza P, Koo TH, Haddix M, et al. SARS-CoV-2 Infection and Hospitalization Among Adults Aged ≥18 Years, by Vaccination Status, Before and During SARS-CoV-2 B.1.1.529 (Omicron) Variant Predominance — Los Angeles County, California, November 7, 2021–January 8, 2022. MMWR Morb Mortal Wkly Rep 2022;71:177–181. DOI: http://dx.doi.org/10.15585/mmwr.mm7105e1

Summary

This study analyzed SARS-CoV-2 infection and hospitalization rates among adults aged ≥18 years in Los Angeles County from November 7, 2021, to January 8, 2022, during the transition from Delta to Omicron variant predominance. The findings highlight that unvaccinated individuals had significantly higher rates of infection and hospitalization compared to fully vaccinated individuals, especially those with a booster dose. The study underscores the importance of COVID-19 vaccination and boosters in reducing severe outcomes and alleviating health care system strain.

Methods

The Los Angeles County Department of Public Health conducted a cross-sectional analysis using COVID-19 surveillance data and the California Immunization Registry 2 (CAIR2). The study included adults aged ≥18 years with laboratory-confirmed SARS-CoV-2 infection. Vaccination status was categorized as unvaccinated, fully vaccinated without a booster, and fully vaccinated with a booster. Age-adjusted 14-day cumulative incidence and hospitalization rates were calculated, and statistical analyses were performed using SAS and R software.

Discussion

The analysis revealed that vaccination, particularly with a booster, significantly reduced the risk of SARS-CoV-2 infection and hospitalization. Despite the rapid spread of the Omicron variant, vaccinated individuals, especially those with a booster, had lower rates of severe outcomes compared to unvaccinated individuals. The study highlights the continued effectiveness of COVID-19 vaccines in preventing severe disease and the critical role of boosters in enhancing protection.

Conclusion

The findings emphasize the importance of staying up to date with COVID-19 vaccinations, including booster doses, to protect against SARS-CoV-2 infection and severe outcomes. Public health efforts should focus on increasing vaccination coverage to reduce the burden on health care systems and prevent COVID-19–associated hospitalizations and deaths.

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