Orange County boasts 70% vaccination rate for adults, but herd immunity is still elusive

People walk on a sidewalk
Orange County had hoped to achieve some herd immunity by the beginning of July.
(Times Community News )

Orange County has hit what both public health officials and experts describe as a significant milestone: 70% of residents 18 and older had received at least one dose of the COVID-19 vaccine as of last week.

The county has been working to get to some level of so-called herd immunity by the beginning of July. That’s gaining more urgency as the new, highly infectious Delta variant is spreading. Delta is now the dominant variant in California, and is blamed for a rise in new cases in L.A. County.

Orange County has nearly 700,000 minors countywide — 65% of whom are under 12 and, consequently, have not been approved to receive the Pfizer-BioNTech vaccine. So does the level of vaccination approach actual herd immunity?


To achieve a 70% threshold among the population at large, considered the low end of herd immunity, nearly 82% of Orange County residents over age 12 would have to be vaccinated or still have sufficient levels of coronavirus antibodies in their systems after recovering from an infection.

The latter is an inscrutable number, as many forego antibody testing. But the county still has a way to go to achieve some semblance of herd immunity.

Vaccination figures from the Orange County Health Care Agency’s online dashboard as of June 30 indicate 58.2% of all residents eligible to receive the COVID-19 vaccine have done so.

Among Orange County’s 3.22 million residents, roughly 55.2% have been fully vaccinated. That number would climb to 62.7% if those who’ve already received the first of a two-dose regimen follow through.

Vaccination rates do increase among older populations, with residents 74 to 84 the most vaccinated, at 91.1%. But the rates among younger groups are considerably lower, with 58.7% of those aged 18 to 24 vaccinated and 43.4% of 12- to 17-year-olds.

Andrew Noymer, a UC Irvine professor of population health and disease prevention, said he’s pleased at the progress Orange County has made so far, especially since adults face greater risk from the coronavirus than children. But, he added, there are caveats.

First-dose vaccine recipients would need to get their second shots, and eligible young people would have to be vaccinated in much higher numbers to safeguard the county from the virus, particularly as more transmissible variants, such as the Delta strain, begin to surface.

“Herd immunity is a moving target. It could be 70%, it could be 85%. [But] the more spreading a strain is, the higher the threshold has to be,” Noymer said. “Seventy percent may not be high enough in the presence of Delta.”

Dr. Regina Chinsio-Kwong, a deputy health officer for the Orange County Health Care Agency, said last week that officials are tracking variant cases in the county, adding that most new infections are occurring among the unvaccinated.


“Data currently shows that those who have been fully vaccinated are protected from serious illness and hospitalization regardless of the variant — this includes Delta,” Chinsio-Kwong wrote in an email. “If someone does get ill with a variant despite full vaccination, there is a small possibility of transmission.”

The county health agency estimates that among the new coronavirus cases being identified, 90% are among residents who have not been fully vaccinated; the unvaccinated account for 95% of the county’s COVID-19 hospitalizations.

Noymer, an authority on epidemiology and public health and an expert on the 1918 influenza pandemic, said the COVID-19 vaccine is significantly more effective than other vaccines used to inoculate against influenza and mumps.

“The COVID-19 vaccines kick ass. Public health has given us the best weapon against this, and that is a great vaccine — now we have to use it,” Noymer said.

“Nobody likes to hear ‘keep going’ when they’re expecting congratulations,” he continued. “But I’m going to say keep going.”

In Los Angeles County, 51% of the population is fully vaccinated. But some 4 million of its 10 million residents have not had a single dose of vaccine. That includes 1.3 million children under 12, who are not yet eligible for the shots.

San Francisco has 68% of its population fully vaccinated, and Santa Clara — Northern California’s most populous county — stands at 66% as of last week.

Cardine writes for Times Community News.