Distribution of the COVID vaccines, which in California is done in several phases and prioritizes first doses for health care workers and people at risk of becoming severely ill from the virus, has lagged other jurisdictions by a considerable margin.

Nationwide, about 6.7 million Americans have received a vaccine dose according to the Centers for Disease Control and Prevention. The CDC has projected that close to 90 million people will be vaccinated by March, still under one third of Americans and far less than the 70% officials say is needed to reach herd immunity.

In California, vaccine rollout has been beset by a number of issues that bring into focus challenges that come with such a gargantuan effort.California has received just over 2 million vaccine doses but only administered about 652,000 of them as of Jan. 8.

Vaccine doses are also lower than anticipated, with officials estimating they won’t have enough doses to immunize “most” residents of its 58 counties until the summer.

Lags are also tied to ultra-low temperature storage requirements for the Pfizer vaccine, a shortage of vaccination sites and staff to administer doses and a delay in setting up systems to track who is immunized and where they live.

The Golden State has the nation’s highest total of people infected with Covid-19, with more than 2.5 million cases. As of Jan. 7, health departments statewide have reported 73,862 positive cases among health care workers and 276 deaths.

California recently told local health departments and providers to expand vaccine eligibility by offering doses to community health and testing site workers, public health field staff and dental clinic and pharmacy personnel.

More than 586,000 health care workers in California have received the first dose of a Covid-19 vaccine, according to state data.

The new guidance also says once demand has subsided from the first priority group, doses should be allocated to people age 75 and older, childcare workers, staff in emergency response and food service and educators.

Los Angeles County, where about 1 in 5 people being tested for Covid-19 are currently testing positive, is the largest from a cluster of Southern California counties that has received about 256,000 doses from the state, the largest quantity of any region. The area includes Orange, San Luis Obispo, Santa Barbara and Ventura counties.

Still, there aren’t enough vaccine doses currently available to immunize even half of the county population by spring, Dr. Paul Simon, chief science officer at LA County’s Department of Public Health, said Friday.

The county said in a statement Friday it opened 19 vaccination sites this week and will open 75 more by next week.