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Nearly 100% of people who contract COVID-19 after close contact with omicron-infected patients are diagnosed within 10 days, investigators say. The new findings support a 10-day quarantine — if other public health considerations warrant it, they contend.

Researchers identified 107 close contacts of two clusters of patients infected with the SARS-CoV-2 omicron variant in November, 2021. All were actively monitored while in quarantine by public health officers, and received reverse transcription PCR tests on days 1, 9 and 13.

Among patients of all ages, 50% were diagnosed on day 3. The average time from exposure to diagnosis was 3.7 days; 70% of diagnoses were made on day 5 and 99.1% were made by day 10, reported ​​Hye Ryeon Lee, of the Korea Disease Control and Prevention Agency in South Korea. 

Quarantine is crucial for slowing the spread of a novel pathogen, Lee wrote. Previous studies have suggested that the omicron incubation period may be shorter than that of the SARS-CoV-2 delta variant, she noted.

Isolation and quarantine are effective public health measures for mitigating the spread of COVID-19, “however, these measures inevitably lead to personal and socioeconomic costs, necessitating evidence-based guidance from policy makers,” Lee said. 

Although a 10-day quarantine period could cover most people who are exposed to omicron, a shorter quarantine duration may be advisable after balancing societal cost with public health benefit, she concluded.

The study was published in the CDC’s Emerging Infectious Diseases.