Mark Pfister, the executive director of the Lake County Health Department attributes the increase to the newer Omicron Variant which is more infectious than previous iterations of the disease.

“Nationwide 73% of the cases are the omicron variant and the number of delta (variant cases) appears to be less,” Pfister said. “When you are near a large population center like Chicago it is likely the omicron variant is now circulating and is a large part of the community transmission.”

New cases grew 30.22% in Lake County over the past week as of Thursday while new infections more than doubled in suburban Cook County during the same time frame as Lake County remains the state’s most vaccinated against the coronavirus pandemic.

There were 440.47 new cases per 100,000 residents in Lake County as of Thursday, a 30.22% bump in the past week, according to the Centers for Disease Control and Prevention website. Of the people eligible to receive the vaccine, 77.5% are fully vaccinated.

In neighboring Cook County, there were 639.33 new cases per 100,000 people, an increase of 107.51%, in the past week, according to the CDC. There 71.3% of people eligible to receive the vaccine are fully vaccinated.

While the percentage growth is less in McHenry County and Kenosha County in Wisconsin, the number of new cases per 100,000 residents is substantially more and less are vaccinated. There were 546.83 new cases per 100,000 people in McHenry and 924.15 in Kenosha, according to the CDC.

Both McHenry and Kenosha Counties trail Lake in vaccinations. In McHenry County, 61.7% have received their shots while in Kenosha 58.8% are completely inoculated. Lake County, at 77.5% leads Illinois followed by DuPage County at 77.1%.

Despite the state leading vaccination rate, Dr. Michael Bauer, the medical director at Northwestern Medicine Lake Forest Hospital, said in an email those who have not yet received their shots should get them. Those who are should get the booster shot.

“One thing that we’ve learned during the pandemic is despite analytic predictive models, the virus is still quite unpredictable,” Bauer said in the email. “As long as individuals remain unvaccinated this pandemic will continue and allow the virus to circulate, infect those susceptible, and unfortunately further mutate.”