The Los Angeles Times reports that the Delta coronavirus variant is now the third-most common in California, new data show, underscoring the danger of the highly contagious strain to people who have not been vaccinated against COVID-19.

The variant makes up 14.5% of California coronavirus cases analyzed so far in June, up from 4.7% in May, when it was the fourth-most identified variant in California, according to data released by the California Department of Public Health.

Experts say the Delta variant poses a greater chance of infection for unvaccinated people if they are exposed. The variant, first identified in India, may be twice as transmissible as the conventional coronavirus strains. It has been responsible for the rise in cases recently in India, the United Kingdom and elsewhere.

But vaccinated people are well protected against infection and illness from the Delta variant. One recent study found that the full two-dose course of the Pfizer-BioNTech vaccine was 88% effective against symptomatic disease caused by the Delta variant and 96% protective against hospitalization.

Los Angeles County, the nation’s most populous, has confirmed 123 Delta variant cases – 49 of them among residents of Palmdale and Lancaster. Fourteen cases of the Delta variant were in people from a single household.

L.A. County data suggest that vaccines are still overwhelmingly effective in protecting people against the Delta variant, as well as other known variants. Of those 123 confirmed cases of the Delta variant in the county, 89% occurred among people who were not vaccinated against COVID-19, and 2% among those who were partially vaccinated. No one has died from the Delta variant in L.A. County.

The few fully vaccinated people who have been infected with the Delta variant “experienced relatively mild illness,” L.A. County Public Health Director Barbara Ferrer said.

Almost everyone who has died in L.A. County of COVID-19 has been unvaccinated. Data released by the county showed that 99.8% of COVID-19 deaths from Dec. 7 to June 7 occurred among unvaccinated people.

“If you are fully vaccinated, you have a lot of protection,” Ferrer said, adding that for the “very small numbers” of people who contracted the Delta variant despite vaccination, “they really did not have serious illness. …This is a pandemic of unvaccinated people.”

The results of outbreaks of the Delta variant elsewhere also support the vaccines’ effectiveness.

Meanwhile, data released by California show that the percentage of the tested population who have antibodies to the coronavirus – a sign of immunity to COVID-19 – is also increasing.

Experts have estimated that 70% to 85% of a population needs to have immunity for a region to develop “herd immunity” to COVID-19, which interrupts the sustained transmission of the virus.

The Delta variant is also spreading nationwide.  From May 9 to May 22, the Delta variant made up less than 3% of analyzed coronavirus samples nationwide. But from June 6 to June 19, that proportion rose to more than 20%.