CDC data estimates 3-day incubation period for Omicron

In an early investigation of the Omicron variant of novel coronavirus, the Center for Disease Control and Prevention (CDC) found a median interval of 73 hours from when infected people were exposed to the variant to when they developed symptoms.

Published in the CDC’s Morbidity and Mortality Weekly Report (MMWR), the study followed a man living in Nebraska who was believed to be the first recorded case of Omicron in the United States. On Dec. 1, 2021, the Nebraska Public Health Library identified six Omicron infections from a household of which one person, the index patient, had recently returned from Nigeria.

The index patient was a 48-year-old unvaccinated man. He had unmasked close contact with five household members. Of the household members, one was double vaccinated with the Pfizer-BioNTech vaccine as of August 2021, three previously had symptomatic COVID-19, and one had symptoms in Nov. 2020 prior to other household members testing positive but received a negative SARS-CoV-2 RT-PRR test, according to researchers

Each household member was symptomatic within 75 hours of exposure to the Omicron variant. The range of symptom onset was 33 to 75 hours, according to the study. The five previously infected patients reported similar or more mild symptoms compared to their first infection. Each patient reported no loss of taste or smell, and two of them reported a subjective fever. The unvaccinated patient who had not been previously infected by COVID-19 experienced joint pain, fever, congestion, chills, and a cough. No one infected required hospitalizations. Four of the twelve close contacts identified by the family consented to COVID-19 tests. None of the tested positive.

According to the CDC’s report, to prevent the formation of new variants and slow transmission, prevention strategies like vaccinations, masking, and social distancing remain important. In addition, fast and widespread genomic surveillance is essential to identify new variants early on.