Top 5 Takeaways

1. Delta Variant Dominance: The Delta variant rapidly increased to 95% of all infections from April 15–July 21, 2021, becoming the predominant variant.
2. Vaccination Status and Variant Distribution: The weekly percentage of variants was similar among fully vaccinated and unvaccinated persons, but the Delta variant was more commonly identified among vaccinated persons overall.
3. Demographic Differences: Delta variant infections were more prevalent among younger persons (18–44 years) and non-Hispanic Black persons.
4. Increased Hospitalization Risk: Among unvaccinated persons, infection with the Delta variant was associated with an increased risk of hospitalization (aHR = 1.81).
5. Importance of Prevention Strategies: Findings reinforce the need for continued monitoring of SARS-CoV-2 variants and implementing multiple COVID-19 prevention strategies, including vaccination.

Original Article Author and Citation

Corresponding Author

Deborah E. Malden, qdz7@cdc.gov

Suggested Citation

Malden DE, Bruxvoort KJ, Tseng HF, et al. Distribution of SARS-CoV-2 Variants in a Large Integrated Health Care System — California, March–July 2021. MMWR Morb Mortal Wkly Rep 2021;70:1415–1419. DOI: http://dx.doi.org/10.15585/mmwr.mm7040a4

Summary

This study analyzed whole genome sequencing data from SARS-CoV-2–positive specimens collected across Kaiser Permanente Southern California (KPSC) from March 4 to July 21, 2021. The study aimed to describe the distribution and risk of hospitalization associated with SARS-CoV-2 variants, particularly the Delta variant, by patient vaccination status. The Delta variant became the predominant variant, with a significant increase in infections among younger persons and non-Hispanic Black persons. The study also found that the Delta variant was associated with an increased risk of hospitalization among unvaccinated individuals.

Methods

Specimens were collected via nasopharyngeal or oropharyngeal swabs, and self-collection of saliva was also available. Whole genome sequencing (WGS) was performed on all positive SARS-CoV-2 test results. Data were linked with patient electronic medical records and analyzed using chi-square tests and Cox proportional hazards regression analysis to compare the distribution of variants and the risk of hospitalization by vaccination status, age, sex, race/ethnicity, and underlying medical conditions.

Discussion

The study observed a rapid shift in the dominant SARS-CoV-2 variant from Alpha to Delta during the study period. The Delta variant was more prevalent among younger adults and non-Hispanic Black persons. The increased risk of hospitalization associated with the Delta variant among unvaccinated persons highlights the importance of vaccination and other preventive measures. The findings align with national and global data on the spread and impact of the Delta variant.

Conclusion

The findings underscore the need for continued surveillance of SARS-CoV-2 variants and the implementation of comprehensive COVID-19 prevention strategies, including vaccination, masking, and physical distancing, especially during periods of high Delta variant transmission.

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