Top 5 Takeaways

1. High Household Transmission: Omicron infection resulted in a high transmission rate of 67.8% among household contacts.
2. Impact of Vaccination: The attack rate (AR) was lower among household contacts of vaccinated index patients, particularly those who received a booster dose (42.7%) compared to unvaccinated index patients (63.9%).
3. Effectiveness of Isolation: Household contacts of index patients who isolated had a significantly lower AR (41.2%) compared to those who did not isolate (67.5%).
4. Mask Use at Home: The AR was lower among household contacts of index patients who wore masks at home (39.5%) compared to those who did not (68.9%).
5. Public Health Recommendations: Multicomponent prevention strategies, including up-to-date vaccination, isolation, and mask use, are critical to reducing Omicron transmission in household settings.

Original Article Author and Citation

Corresponding Authors

Julia M. Baker, nwk0@cdc.gov; Jasmine Y. Nakayama, qdt2@cdc.gov

Suggested Citation

Baker JM, Nakayama JY, O’Hegarty M, et al. SARS-CoV-2 B.1.1.529 (Omicron) Variant Transmission Within Households — Four U.S. Jurisdictions, November 2021–February 2022. MMWR Morb Mortal Wkly Rep 2022;71:341–346. DOI: http://dx.doi.org/10.15585/mmwr.mm7109e1

Summary

The study examined household transmission of the SARS-CoV-2 Omicron variant in four U.S. jurisdictions from November 2021 to February 2022. The investigation found high transmission rates within households, especially among those with unvaccinated index patients or those who did not practice isolation and mask use. The findings underscore the importance of multicomponent prevention strategies to mitigate the spread of Omicron in household settings.

Methods

Participants with sequence-confirmed Omicron infections and their household contacts were identified and interviewed. The study assessed household transmission rates and the effectiveness of various prevention measures, including vaccination status, isolation practices, and mask use. Attack rates were calculated and compared across different strata using statistical methods to account for clustering by household.

Discussion

The investigation revealed that Omicron led to high transmission rates within households, particularly among those with unvaccinated index patients or those who did not follow preventive measures. The findings highlight the critical role of vaccination, isolation, and mask use in reducing transmission. The study also noted limitations, including reliance on self-reported data and potential biases in the sample.

Conclusion

The study reinforces the importance of implementing multicomponent prevention strategies, such as up-to-date vaccination, isolation of infected persons, and mask use at home, to reduce the transmission of the Omicron variant within households. These measures are essential to protect household members, especially those who are unvaccinated or unable to follow certain preventive practices.

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