OKLAHOMA CITY (AP) — An Oklahoma doctor warned Thursday that an increase in coronavirus cases in the state could be the precursor to another surge of the illness.

The seven-day average of new cases in the state has increased 90% since June 7, from 99 new cases daily to 190, based on Oklahoma State Department of Health data, according to OU Health Dr. Dale Bratzler,

Bratzler, who heads the University of Oklahoma’s coronavirus response, said a virus outbreak in neighboring southwest Missouri is likely a prime cause of a surge in Oklahoma.

“I think that delta (variant) that's causing the big outbreak in southwest Missouri is making its way down (Interstate 44)” and into neighboring northeastern Oklahoma, where the most new daily virus cases are occurring, Bratzler said.

Bratzler said Tulsa County, the state's second most populous, in northeast Oklahoma has had 259 new cases in the past week while Oklahoma County, the most populous, in central Oklahoma had 85.

The state health department has reported 41 confirmed cases of the delta variant, a fast-spreading mutation of the virus that potentially makes people sicker.

Bratzler said studies have shown that full doses of the Pfizer and the Moderna virus vaccines are about 88% effective against the virus.