Workers prepare Covid-19 tests at a Nomi Health testing site in Omaha, Nebraska.
An investigation into a cluster of omicron infections in Nebraska suggests that the heavily mutated variant has a shorter incubation period and causes similar or milder symptoms compared to the past variant for people who are vaccine-vaccinated.
Six omicron cases were confirmed from a single household in Nebraska, and the CDC released findings from an epidemiological investigation.
A man who returned to the U.S. from a conference in Nigeria tested positive for the disease a day later. The man who was unvaccinated and had a history of symptoms of an infectious disease reported that he was not wearing a mask when he had a close contact with a masked person at the international conference.
The results of the test the man took before he returned to the U.S. came back negative. He was symptom free after returning to the U.S., and had close contact with five members of his household in Nebraska without wearing a mask.
The five members of his household, at least one of whom was as young as 11 years old, developed symptoms and tested positive. Four of them had previous histories of symptoms of a disease, one of which was fully vaccineed with two Pfizer doses.
An unvaccinated person in the household tested positive for Covid for the first time. The person had mild upper respiratory symptoms in November 2020 before the other members of the household got sick.
The CDC said it took 33 to 75 hours for household members to show symptoms after exposure to the man who traveled, suggesting a shorter incubation period with omicron. According to the CDC, the median incubation period for Covid is 5 days or more, while the delta variant takes about 4 days for symptoms to show.
According to the CDC, the household members who were reinfected experienced less symptoms than the first time. Two of them reported a mild case of the flu, but no loss of taste or smell.
The unvaccinated individual had not tested positive before they had a bad cough, joint pain, congestion, fever and chills. None of the people in the household had underlying health conditions or compromised immune systems after they tested positive for omicron. After their first infections in 2020, the re-infecting people did not need hospitalization.
The first case of omicron was reported in the San Francisco area. The individual had traveled to South Africa. The variant could have arrived in the U.S. earlier, as the CDC found someone who reported symptoms after international travel.
Omicron was first identified by two countries. The variant now makes up 42% of the cases in the US.
A growing body of data from South Africa and the United Kingdom shows that people don't get as sick from omicron compared to the delta variant. The U.K. Health Security Agency found that people with omicron were less likely to be hospitalized. Scientists in South Africa found that people with omicron were 70% less likely to get a disease.
The authors of the studies cautioned against reading too much into the preliminary data, because it could be that vaccine and immunity from prior infections influenced the findings.
The U.K. Health Security Agency found that a booster dose of Pfizer and BioNTech's vaccine provides 75% protection against disease from omicron. Two-doses of the Pfizer vaccine are less effective at preventing omicron infections than one dose, according to data from South Africa.
There are new Covid cases in the U.S. CNBC analysis of data from the University shows that the number of new cases in the country has increased by more than half over the past week.
Over the past week, the number of people hospitalized with Covid has risen by 3%.
