For weeks, experts have warned that the highly infectious delta variant would become the dominant coronavirus strain in California.
Now the latest data show their prediction has come true. According to the state’s variant tracker, the delta variant, first identified in India, has gained momentum and accounted for 35.6% of cases sequenced in June. That’s a big jump from May, when it accounted for only 5.6% of cases sequenced, and April, at 2.1%.
Until now, the alpha variant, which originated in the United Kingdom, was the dominant variant. It accounted for 34.3% of cases sequenced in June, down from 58% in May and 50.1% in April.
Before that, California’s homegrown epsilon variant was the primary strain, making up 50.2% of cases sequenced in March, 59.1% in February and 49.3% in January. Now, the epsilon variant makes up just 1.9% of specimens sequenced in California.
The Pfizer and Moderna vaccines have proved highly effective against the delta variant, and on Thursday Johnson & Johnson said its single-dose vaccine also provides a “strong, persistent” immune response against the strain.
That leaves the unvaccinated population particularly vulnerable to the delta variant, which is estimated to be 75% more contagious than the original coronavirus. On Friday, Dr. Grant Colfax, director of the San Francisco Department of Public Health, said the delta variant accounts for 30% of local cases now, but he expects it to increase to 90% in the next few months.
“This is not a good time to be unvaccinated in San Francisco,” Colfax said. “People may have the misperception that because our vaccine rates are high, even if they’re not vaccinated they are unlikely to catch the virus. I think delta has shifted the equation.”
The state lifted most coronavirus restrictions on June 15, including allowing vaccinated people to go maskless in most indoor settings. However, amid rising concerns about the delta variant, Los Angeles County last week strongly urged all residents to voluntarily wear masks indoors in public places, including those who are fully vaccinated.
However, state health officials said they were not yet ready to make a similar recommendation. Bay Area health agencies said they are following the state’s lead for now and remain focused on encouraging those who are eligible to get vaccinated.