Top 5 Takeaways

1. Delta Variant Predominance: The Delta variant became the predominant SARS-CoV-2 strain in the U.S. by mid-June 2021, leading to increased COVID-19-associated hospitalizations.
2. Severity of Outcomes: No significant increase in severe outcomes (ICU admission, mechanical ventilation, in-hospital death) was observed among hospitalized COVID-19 patients during the Delta period compared to the pre-Delta period.
3. Unvaccinated Younger Adults: The proportion of hospitalized unvaccinated adults aged 18–49 years significantly increased during the Delta period, highlighting lower vaccination rates in this age group.
4. Vaccination Coverage: Lower vaccination coverage in adults aged 18–49 years likely contributed to the increase in hospitalizations during the Delta period.
5. Public Health Implications: COVID-19 vaccination remains critical for all eligible adults, especially those under 50 years old who have lower vaccination rates compared to older adults.

Original Article Author and Citation

Corresponding Author

Christopher A. Taylor, cataylor1@cdc.gov

Suggested Citation

Taylor CA, Patel K, Pham H, et al. Severity of Disease Among Adults Hospitalized with Laboratory-Confirmed COVID-19 Before and During the Period of SARS-CoV-2 B.1.617.2 (Delta) Predominance — COVID-NET, 14 States, January–August 2021. MMWR Morb Mortal Wkly Rep 2021;70:1513–1519. DOI: http://dx.doi.org/10.15585/mmwr.mm7043e1

Summary

This study analyzed data from the CDC COVID-19–Associated Hospitalization Surveillance Network (COVID-NET) to examine trends in severe outcomes among adults hospitalized with COVID-19 before and during the Delta variant predominance. Despite the increased transmissibility of the Delta variant, no significant increase in severe outcomes (ICU admission, mechanical ventilation, in-hospital death) was observed. However, the proportion of hospitalized unvaccinated adults aged 18–49 years significantly increased during the Delta period, likely due to lower vaccination rates in this age group.

Methods

Data were collected from COVID-NET, which conducts population-based surveillance for laboratory-confirmed COVID-19–associated hospitalizations in 99 counties across 14 states. Hospitalization rates were calculated by dividing the total number of hospitalized COVID-19 patients by population estimates within each age group. Clinical outcomes data were collected on a representative sample of hospitalized adults, excluding pregnant women. Severe outcomes assessed included ICU admission, receipt of invasive mechanical ventilation (IMV), and all-cause in-hospital death. Statistical analyses were conducted using SAS statistical software.

Discussion

The analysis found no significant changes in severe outcomes among hospitalized COVID-19 patients between the pre-Delta and Delta periods. However, the proportion of unvaccinated adults aged 18–49 years hospitalized with COVID-19 increased during the Delta period, reflecting lower vaccination coverage in this age group. These findings align with previous studies and highlight the importance of increasing vaccination rates among younger adults to reduce hospitalizations.

Conclusion

Although the Delta variant is more transmissible, it did not lead to significantly higher proportions of severe outcomes among hospitalized adults. The increase in hospitalizations among unvaccinated younger adults underscores the need for targeted vaccination efforts in this age group. COVID-19 vaccination is crucial for all eligible adults to mitigate the impact of the Delta variant and future variants.

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