Topeka — Kansas on Friday reported its biggest surge in COVID-19 cases in more than three months with the faster-spreading delta variant becoming a growing public health issue.

Some of the biggest numbers of new cases per 1,000 residents over the previous two weeks were in counties bordering Missouri, where cases have spiked recently because of the delta variant. Both states also have seen vaccinations slow amid some residents’ resistance to getting vaccinated.

Kansas had an average of 275 new COVID-19 cases a day for the seven days ending Friday, according to state Department of Health and Environment data. That was the highest seven-day average for new cases in 15 weeks, since March 26.

Kansas officials had worried ahead of the Fourth of July weekend that many of the state’s residents would travel, particularly to Missouri, and bring coronavirus variants back with them. But border county residents travel into Missouri regularly for jobs, shopping, medical care and fun.

“And then also then people work over here in our county from Missouri,” said Betha Elliott, the health department administrator in Cherokee County, in the state’s far southeast coroner.

The number of new cases per day is still far below its peak in mid-to-late November, but it comes after local officials ended mask-wearing mandates and leaders of the Kansas Legislature ended a state of emergency for the pandemic.

State health department data showed that Cherokee County had the largest number of new cases per 1,000 residents over the past two weeks of any of Kansas’ 105 counties, 6.67, more than six times the state’s figure of 1.08 new cases per 1,000 residents. Cherokee County has almost 20,000 residents, and the state reported 133 new confirmed or probable cases there during the past two weeks.

The top 20 counties for new cases per 1,000 residents included seven of the 10 counties bordering Missouri. Another four are in southeast Kansas — relatively close to the delta variant hotspot of southwest Missouri.

Kansas health department data showed that the number of confirmed cases of the delta variant jumped 44.1% from Monday to Friday, up 158 to 516 since the first was confirmed in May. Confirming cases of variants requires genetic testing of patients’ nasal swabs or saliva samples, but both state and U.S. health officials believe most new cases in Kansas or Missouri are from the delta variant.

“We have offered assistance to local health departments and are sending added resources for testing and vaccination to the most affected areas,” Dr. Lee Norman, the state health department’s top administrator, said. “We continue to advise that vaccination and mask wearing increase.”

Norman, like other health officials, said existing vaccinations are effective against the delta variant. But Kansas averaged about 7,200 shots a day for the seven days ending Friday, well below the peak average of more than 29,000 shots a day for the seven days ending April 7.

The state health department reported that 39.4% of Kansas’ 2.9 million residents were fully vaccinated as of Friday.