Output of a California state model showing predicted herd immunity for Santa Cruz County.
Output of a California state model showing predicted herd immunity for Santa Cruz County.
(California Department of Public Health)
COVID Today

Green tier? County could enter orange tier in three weeks, herd immunity possible by late spring

In a press conference Thursday, county health officer Dr. Gail Newel said the county and state could reach some level of herd immunity by mid-May.

County health officer Dr. Gail Newel shared a cornucopia of hopeful news in Thursday’s COVID-19 update: Santa Cruz County is on track to enter the orange tier in three weeks, a spring surge no longer appears imminent, and it’s possible California could reach herd immunity by late spring.

The county is seeing “continued good news in terms of case rates, hospitalizations, death rates, [and] ICU availability,” Newel said, adding that she expects the county to progress quickly from the orange to the yellow tier, and even into the green tier (which doesn’t currently exist but Gov. Gavin Newsom has said is in the works).

The previously predicted surge in late March or early April also appears less likely, according to county health officials, who consult a model that includes the impact of variants and vaccines.

“At this point, the model is showing that there may be a slight plateau towards the end of the month, but very unlikely a surge,” Newel said. “We haven’t had the influx of the B.117 variant into California that we thought we might have.”

Newel and Dr. David Ghilarducci, the county’s deputy health officer, shared results from forecasting models that raise the hopeful possibility that California and Santa Cruz County could reach some threshold of herd immunity by late spring or early summer, which is sooner than had been previously predicted by most experts.

Despite the uniformly positive forecasts shared in today’s update, Newel said she was concerned about opening the economy so quickly, at the same time as schools are opening and some people may be planning to travel over spring break. She also conceded that COVID-19 is a mysterious disease, and it’s far too early to declare victory.

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“We don’t fully understand why the disease curve has so dramatically decreased, why we’ve seen an even sharper decrease in case rate than we did see rise [in the fall],” Newel said. “It may be that this virus has a seasonal component and that we may be seeing an annual surge in the future.”

Officials hope the surge will not be as large as what has happened over the course of the past year, as people have more immunity from vaccines and past infections. But many uncertainties remain about how long immunity to the disease will last from either of those things, especially as new variants continue to proliferate.

In light of these unknowns, Newel said that, although she remains “very hopeful, it’s a cautious optimism.”