How did California go from the epicenter of the US pandemic to the lowest statewide transmission rate?

How did California go from the epicenter of the US pandemic to the lowest statewide transmission rate? The state has some of the strictest vaccine mandates and masking policies. ABC News ABC News

With the lowest COVID-19 infection rate among all states as of Friday, California, which has some of the strictest mask and vaccination mandates in the country, has managed to flip the script as the former U.S. epicenter of the pandemic.

"They've been very much forward-thinking in terms of policies around vaccination requirements and mandates," said epidemiologist Dr. John Brownstein, chief innovation officer at Boston Children's Hospital and an ABC News contributor.

As of Friday evening, California had an infection rate of 61.1 cases per 100,000 over the past week, according to data from the Centers for Disease Control and Prevention. The state was briefly the only to be classified with a "moderate" rate of transmission -- 10 to 49.99 cases per 100,000 over seven days -- before it went back up to "substantial," meaning 50 to 99.99 cases per 100,000 over seven days.

Over the previous week, Hawaii, Florida, Louisiana, Connecticut, New Jersey, Mississippi, Maryland, Georgia and Washington, D.C., each also reported "substantial" rates.

A rate of at least 100 cases per 100,000 is labeled as "high." Montana, Wyoming, Idaho and Alaska, as of Friday, had the highest rates over the previous seven days, with each above 450 cases per 100,000 people. The U.S. average over that span was 150.9.

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Experts said California's journey from worst to first is likely due to a combination of things.

"We can't know for sure which factors are responsible," Brownstein added, "but we know that the combination of interventions and policies can play a really strong role in driving transmission."  ...