COVID-19 updates: 70% of American adults fully vaccinated

The U.S. is at an "inflection point" heading into the colder winter months, the PolicyLab at Children’s Hospital of Philadelphia said this week in its latest COVID-19 forecast. 

Throughout the fall, increases in case incidence were mostly concentrated in areas with poor vaccination rates, such as in communities across Alaska, Idaho, Michigan, Montana, Utah and Wyoming. However, there is growing concern among experts that both colder weather and an increase in indoor gatherings, such as over Halloween weekend, will "further drive increases in COVID-19 transmission over the next couple of weeks."

The U.S. is likely at a critical moment for more highly vaccinated areas with colder weather and holiday gatherings approaching, according to the group.

"The coming weeks will reveal whether other highly vaccinated regions in the West, Midwest, and Northeast can maintain steady incidence rates -- and more importantly stable or declining hospitalizations -- amidst the increasing pressure of even colder weather and more gatherings," experts wrote.

-ABC News' Arielle Mitropoulos

Despite boasting high vaccination rates, several Northern states, particularly in the Upper Midwest and the Northeast, continue to see their case numbers tick up as the weather gets colder, according to federal data.

Alaska currently has the country's highest infection rate, followed by Montana, North Dakota and Wyoming.

The U.S. daily death average, though down from 1,800 deaths reported each day in September, remains around 1,100 – which is nearly six-times higher than mid-June, according to federal data.

-ABC News' Arielle Mitropoulos

Indiana Gov. Eric Holcomb said he's directing the state's labor department to "work with the Attorney General on a lawsuit challenging the federal government" in the wake of the Biden administration's announcement that large businesses must begin enforcing a vaccine-or-test mandate Jan. 4.

Holcomb in a statement Thursday called Biden's plan "an overreach of the government’s role."

"While I agree that the vaccine is the tool that will best protect against COVID-19, this federal government approach is unprecedented and will bring about harmful, unintended consequences in the supply chain and the workforce," he said.

Nebraska Gov. Pete Ricketts also said he'd "fight" the mandate.

"If this rule is allowed to take effect, many Nebraskans will be at risk of losing their jobs over something that should remain a personal health choice," Ricketts said in a statement. "I have been in communication with the Attorney General today, who will be taking the lead on Nebraska’s legal review of the potentially illegal federal vaccine mandate. We will fight back."

The vaccine mandates for businesses with 100 or more workers is a part of a sweeping new federal plan that identifies COVID-19 as an occupational hazard in the workplace. Industry groups had pressed the administration to give businesses extra time, warning that imposing any mandates now would exacerbate the nation’s worker shortage. The plan gives federal contractors an extra month to comply, sliding back the previously-set Dec. 8 deadline.

As Dr. Anthony Fauci and CDC director Rochelle Walensky testified Thursday before the Senate Health, Education, Labor, and Pensions Committee, they spoke to the vaccine mandate that'll soon be in effect for businesses with 100 or more employees.

Walensky said, "We know the most disruptive thing in our workforce is to have a COVID outbreak and to have workers in that workforce come down with COVID infection, severe disease, and in some cases, death."

"Vaccination, as we've seen, decreases your risk of infection by sixfold, decreases your risk of hospitalization and death by tenfold -- even during this delta surge. So there's absolutely a public health priority to get people vaccinated and to continue the important prevention and mitigation strategies including masking to keep them safe," she said.

-ABC News' Cheyenne Haslett