The omicron coronavirus variant is now the dominant strain in the U.S., accounting for 73.2 percent of new infections for the week ending Dec. 18.
Here are six other COVID-19 updates to know from the last week:
1. Omicron might have an average incubation period of three days, shorter than any variant, according to preliminary findings from studies.
2. President Joe Biden on Dec. 21 announced initiatives his administration is rolling out as omicron contributes to a surge in COVID-19 cases in the U.S.
3. California will require that healthcare workers receive a COVID-19 booster, Gov. Gavin Newsom said Dec. 21. The announcement, which came after California issued an order Aug. 5 requiring workers in healthcare settings to be fully vaccinated, is part of new state actions amid a COVID-19 surge.
4. Over the last week, seven-day COVID-19 case averages have risen in 33 states, flattened in four and dropped in 13, according to data tracked by Baltimore-based Johns Hopkins Coronavirus Resource Center. Here are 33 states where cases are rising.
5. Vermont has the highest rate of fully vaccinated people getting boosters, according to the CDC's COVID-19 vaccine distribution and administration data tracker. Here are states ranked by booster rates as of Dec. 22.
6. Omicron, which World Health Organization officials warned is spreading faster than any COVID-19 vari