(CNN/AP) — Due to the surge of Covid-19 cases, the director of the US Centers for Disease Control and Prevention is asking unvaccinated Americans not to travel during the Labor Day holiday weekend.

The US is surpassing an average of 160,000 new cases a day, according to data from Johns Hopkins University. With the spread of the more transmissible Delta variant and many students returning to the classroom for a new academic year, the rise is concerning officials and health experts.

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“First and foremost, if you are unvaccinated, we would recommend not traveling,” CDC Director Dr. Rochelle Walensky said at a White House Covid-19 Response Team Briefing on Tuesday.

Walensky said that while people who are fully vaccinated can travel with precautions, current transmission rates mean they, too, need to take Covid-19 risk into consideration when deciding whether to travel.

Health experts have said that vaccination is the best way to protect against the virus’ spread, and many have attributed the spike in cases to the large portion of Americans who are unvaccinated.

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Of those eligible for vaccinations, which includes Americans 12-years-old and older, 38.5% are not fully vaccinated, according to data from the CDC.

This week, data presented by a CDC vaccine adviser showed a hospitalization rate 16 times greater in the unvaccinated population than in those vaccinated. And the surge in hospitalizations, particularly among unvaccinated people, has stretched hospitals thin.

Pennsylvania is now averaging more than 3,200 new and confirmed COVID-19 cases daily, about 20 times the number of infections it was reporting in early July. More than 1,700 people are hospitalized, up sevenfold since last month. Nearly 6 million people are fully vaccinated.

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