Omicron may have an average incubation period of three days, shorter than any variant yet, according to preliminary findings from studies cited by The Atlantic.
Six things to know:
1. The exposure-to-symptom gap, called the incubation period, is estimated to be about five to six days for the original strain, five days for the alpha variant and four days for delta.
2. A research paper published Dec. 16 by Eurosurveillance describes an outbreak involving 80 people at a restaurant in Norway. Nearly every person who had omicron said they were vaccinated and had received a negative antigen-test result within two days before the party. After the event, symptoms appeared in about three days. This suggests the virus had multiplied so quickly that rapid-test results had been rendered obsolete. Almost all individuals reported at least one symptom and more than half (54 percent) reported fever.
3. The research findings from Norway are preliminary and might not represent the general population, though they appear to match with other early, sometimes-anecdotal reports, according to The Atlantic.
4. Ajay Sethi, PhD, epidemiologist at the University of Wisconsin-Madison, still wants more data before asserting omicron has a shorter incubation period, he told The Atlantic. But "it does make sense," Dr. Sethi said, considering the variant's explosive growth. Omicron has quickly become the dominant strain in the U.S., accounting for 73.2 percent of new infections for the week ending Dec. 18, according to CDC data. That's up from 13 percent from the week ending Dec. 11.
5. "If omicron has a shorter incubation period, that's going to wreak havoc on how we test for it and deal with it," Omai Garner, PhD, director of clinical microbiology at UCLA Health, told The Atlantic. As the virus travels more rapidly, it will also get harder to control.
6. Incubation periods might differ by vaccination status, underlying health conditions, infection history, age and the amount of viral load people face.