The Centers for Disease Control and Prevention this week said the highly contagious delta strain of COVID-19 first spotted in India is now a “variant of concern” in the U.S. And the variant is becoming more common in Arizona.

Nearly 70% of recent COVID-19 cases in Arizona have been from the alpha variant first spotted in the U.K. The delta variant is estimated to be 60% more contagious than alpha. TGen North, the lab sequencing the largest share of COVID-19 test samples in the state, first spotted the delta variant in Arizona in May. Now, delta already appears in more than 2 percent of test samples, according to TGen data. 

“This is what happens, especially toward the end of a pandemic, you have fewer and fewer people that are susceptible. The viruses that spread the fastest are going to be the ones that survive in the end. And that’s why we’re seeing this delta variant,” said David Engelthaler, co-director of the Pathogen Genomics Division at TGen North.

The delta variant quickly outcompeted the alpha variant to become the dominant strain in the U.K. and Engelthaler expects the same will happen in Arizona. 

“It’s out there, it’s prevalent, and that’s why people really should be vaccinated," Engelthaler said. 

Vaccines are still effective against the delta variant. Research indicates the Pfizer and Moderna vaccines provide 88% protection against it, but only with both doses. A single dose is only about 33% effective against the delta variant. 

Arizona’s rate of vaccination remains below the national average, with about 39% of residents fully vaccinated.