In-Depth: Why California has lowest COVID-19 transmission rate in the US

Vaccines, culture help state keep COVID at bay
Posted at 6:11 AM, Oct 08, 2021
and last updated 2021-10-08 13:38:40-04

SAN DIEGO (KGTV) - California reached the CDC's "Moderate" tier for COVID-19 transmission and infections earlier this week. That's the second-lowest of the CDC's four-tiered system to measure the spread of the disease on a state-by-state basis.

According to the CDC, on Oct. 4, California had only 41.3 COVID-19 cases for every 100,000 people on a 7-day average.

States need to have between 10 and 49.99 cases per 100,000 people to be in the "Moderate" tier.

California has since slipped back into the "Substantial" tier, but it still leads the nation for case rates.

Connecticut is the only other state in the "Substantial" tier. All other states and the District of Columbia are in the "High" transmission tier.

ABC 10News spoke with Dr. Eyal Oren, the Interim Director at San Diego State University's School of Public Health, about why California is doing so well, even as other states struggle to keep case numbers down.

"I think the first reason, and maybe the one that's most obvious, is the high rates of vaccination that we've seen in California," Dr. Oren says.

Right now, California has 59% of its total population fully vaccinated. That's only slightly higher than the national average of 56.4%. Still, Dr. Oren says that goes a long way towards protecting everyone.

"Case rates, hospitalization rates, death rates are all much much lower among people who are vaccinated compared to unvaccinated," he says.


Still, California's vaccination effort ranks 15th among the U.S. states, even as its case rate ranks first.

Dr. Oren thinks it's more about where vaccinations take place than just the overall number. He points to California's major population centers, which have significantly higher vaccination rates than the state overall, as reasons for success.

"We know this is an easily transmissible disease," says Dr. Oren. "So wherever you have greater cores of the density of people, you're also likely to have the potential for transmission... and vaccination can really help in terms of stopping transmission," says Dr. Oren.

Listen to Jared Aarons' full interview with Dr. Eyal Oren below:

According to county data, San Diego County has 79.4% of its population fully vaccinated, Alameda County has 78.6%, San Francisco County has 75%, and Los Angeles County has 69%.

Dr. Oren says higher than average numbers in those densely populated areas can help the entire state keep case numbers down, even as smaller counties lag in vaccines.

Beyond vaccine numbers, Dr. Oren says vaccine enforcement and other public health mandates have helped California stay ahead of the virus.

Currently, California requires vaccines for healthcare workers, state public employees, and teachers and staff at schools. Gov. Newsom says students will soon be required to get a vaccine as well.

Meanwhile, renewed mask regulations over the summer reminded people the listen pandemic hadn't ended. Many indoor places require masks. And a new state regulation requires vaccines or a negative COVID test for "mega" events with more than 1,000 people indoors or 10,000 people outdoors.


Several counties have also tightened vaccine and mask requirements in recent weeks.

"California is quite proactive in terms of how it's engaged with vaccination and some of the policy and regulatory requirements," says Dr. Oren. "I personally saw how that changed the conversation. People thought differently about those indoor environments. It was a quick shift."

The state's climate and geography have also helped. listen California's outdoor culture allowed more people to spend a significant amount of time outside, where they can be socially distanced and safe.

"We know that being outside allows for a greater dispersal of viral particles," says Dr. Oren. "We know that ultraviolet light kills many viruses and bacteria, including COVID."

All of that has combined, says Dr. Oren, to help California achieve the lowest transmission rate in the country. Now Dr. Oren says the people in the state need to listen continue their vigilance to avoid another dramatic rise.

"I would argue as individuals we can be more careful in the ways we interact and what we do," he says. "That doesn't mean not going out and not doing anything. It's just being aware of your surroundings."