Since Jan. 20, 2020, when health officials reported the first local fatality from COVID-19 — involving a man who had just come back from Wuhan, China — the still-mysterious and evolving disease has gone on to kill more than 7,700 people in Orange County, making it the most lethal health event of the past century.

But according to three years of local health data, COVID-19 has been something else as well — an unequal-opportunity killer.

Odd inequities

In the first two years of the pandemic (numbers for 2022 aren’t complete), COVID-19 was the third-leading cause of all deaths in the county, according to data from the Orange County Health Agency. For older residents, ages 65 and up, it was the third-leading cause of death, ahead of Alzheimer’s among others. And for local Latinos, COVID-19 was the No. 1 cause of death.

But those inequities only hint at the random way the worst outcome of the disease has played out in different parts of Orange County.

Consider: In Irvine, a city of 309,031 people, roughly one out of every 1,652 residents has died of COVID-19 since the start of 2020, according to county numbers through Dec. 30, 2022. But in Santa Ana, a neighboring city with almost exactly the same-sized population (309,441), the death rate has been about six times higher, roughly one out of every 271 residents.

Such discrepancies are common in a county with 34 cities and nearly as many distinct economic, social and demographic realities.

Laguna Woods and Seal Beach — two communities defined or shaped by the age of their residents — have suffered COVID-19 death rates nearly 10 times higher than the city that’s suffered the lowest death rate, Laguna Beach. But cities without age-centric populations show similar differences. The death rate in La Habra, for example, has been roughly three times higher than in Tustin, even though both cities are similar in median age, population size and household income.

Not just biology

Such gaps are only partly about biology. Instead, public health experts say three years of COVID-19 mortality has simply exposed the sharp social and economic inequalities that existed in the county long before the pandemic.

“The characteristics of people living in different places influence both the likelihood that they are tested for COVID-19 and their risk of severe disease if they are infected with the virus,” said epidemiologist Dan Parker, an assistant professor of population health and disease prevention at UC Irvine who co-wrote a 2021 study that looked at different COVID-19 death rates in Orange County during the early months of the pandemic.

“It isn’t that the virus was different,” he added, via email. “It’s the demography, biology, and socioeconomic conditions of the population that are different.”

The factors that drive the worst outcome of COVID-19 in a particular community, Parker and others say, are still coming into focus.

Community factors

Public health experts point to a few specific community characteristics — median age, population density and access to insurance — as part of a constellation of reasons why death rates are so uneven in Orange County.

“In all communities, it’s disproportionately older people who die of COVID,” said Andrew Noymer, an associate professor at UC Irvine who teaches about population health and disease prevention. “Obviously, anybody can die of the disease. And many factors are part of this. But age is the real risk factor.”

That’s certainly true in isolated places, such as nursing homes, where COVID-19 deaths are much higher than other parts of the population. And it’s been true for individuals as well, as numerous studies have found that COVID-19 death rates jump considerably with each decade of life.

But it’s not at all clear that age, on its own, is the biggest reason why COVID-19 deaths have been higher in some Orange County cities than in others. Census data shows the ages in cities that suffered more COVID-19 deaths, and those that suffered fewer, were roughly the same.

Multigenerational living

Another factor driving COVID-19 deaths, on a city-by-city basis, is population density, at least when “density” reflects the number of people living under the same roof. People packed together, indoors, boosts the spread of most communicable diseases, including COVID-19.

“Multigenerational living is a huge factor in this,” said Noymer. “It’s another key to the puzzle that definitely dovetails with (COVID-19) mortality.”

That’s backed up by the numbers. Census data shows that in the 19 cities with lower-than-average death rates, the number of people per household is 2.75, or about 10% less dense than the 2.99 people per household in the 15 other cities where COVID-19 deaths have been higher than average.

Health care access

Another factor is access to health care.

Though viral testing and, later, vaccines have been free to the public through federal or state agencies over the past three years, community health in some Orange County communities was compromised long before the arrival of COVID-19. And given that COVID-19 is far more likely to be lethal when a person suffers from other health problems experts believe a community’s pre-pandemic access to health care played a powerful role in differing death rates.