Highly-mutated COVID strain spiking in California — here’s where clusters have formed
Health officials in California are monitoring a newly emerging COVID-19 variant known as “Cicada,” which has been detected in clusters in San Francisco and Kern County.
Researchers say the Cicada variant is a heavily mutated subvariant that has recently begun circulating in parts of the state. Scientists believe it has gained attention because its mutations may help it partially avoid immune protection built from previous infections and vaccinations.
The variant is appearing at a time when COVID-19 has begun to follow an unusual seasonal pattern in California. Over the past two years, the virus has produced larger waves during the warmer months rather than in winter, a shift from what was commonly seen earlier in the pandemic.
Dr. Neil Silverman, who leads the Infections in Pregnancy Program at the David Geffen School of Medicine at UCLA, said the timing of the new strain could align with the state’s emerging summer pattern for COVID activity. He noted that the virus does not behave in the same predictable seasonal way as influenza.
The name “Cicada” comes from the insect known for disappearing for long stretches before suddenly emerging again. Scientists used the nickname to describe how the variant appeared to remain relatively quiet before resurfacing in monitoring data.
During recent winters, influenza has been responsible for a larger share of respiratory illness cases while COVID-19 activity has increasingly shifted toward summer months. Researchers writing in the Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report said that although immunity from prior infections and vaccinations has lowered the rate of severe disease, COVID-19 still poses a meaningful public health concern.
California health authorities are encouraging people at higher risk—especially older adults and individuals with weakened immune systems—to stay current with updated COVID-19 vaccinations. Officials recommend two updated doses spaced six months apart for those in these higher-risk groups.
Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco, warned that low vaccination coverage among seniors is a major vulnerability. He said confusion and disagreement surrounding vaccines have contributed to lower uptake and have sometimes caused people to view COVID-19 through a political lens rather than as a public health issue.
Scientists first identified the Cicada subvariant outside the United States in late 2024. It later appeared domestically through international travel. Since that time, the variant has been detected in several countries and states.
According to Alexandria Boehm, a professor of civil and environmental engineering at Stanford University, public health teams have tracked the variant through wastewater testing and screening of international travelers. These surveillance systems allow researchers to identify viral changes before large outbreaks occur.
In California, traces of the Cicada variant have been detected in sewage monitoring data, though its overall presence remains relatively low. Experts say the strain has not yet been associated with more severe illness, but its genetic changes make it different enough from earlier variants to warrant close observation.
Forecasts currently suggest that any increase in cases later this summer or early fall would likely be gradual rather than a sharp spike. Still, specialists say vaccination coverage remains a concern, particularly among older residents who face the highest risk of serious illness.
Health data show that fewer than one-third of California seniors have received the most recent updated COVID vaccine. This leaves a large portion of that age group more vulnerable if infections rise again.
Medical experts stress that vaccines still provide strong protection against hospitalization and severe disease. They also point out that vaccination may reduce the risk of long COVID, a condition in which symptoms persist long after the initial infection. Repeated infections can raise the chances of developing these long-lasting complications.
Dr. Chin-Hong compared the situation to watching a developing storm. He said it is unclear whether the variant will produce a significant increase in cases or simply pass without major impact, but it is enough to prompt caution among public health officials.
COVID-19 first appeared in late 2019 and was confirmed in the United States on January 20, 2020. Since then, the virus has caused more than 1.1 million deaths in the U.S. and at least 7 million worldwide. The virus responsible, SARS-CoV-2, has continued to evolve into numerous variants throughout the pandemic.
The CDC states that COVID-19 spreads mainly through respiratory droplets and aerosols released when infected people breathe, talk, cough, or sneeze. Transmission is more likely in crowded or poorly ventilated indoor environments, and individuals can spread the virus even if they do not show symptoms.
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