State after state has been reporting more cases of COVID-19, and health experts say it's possible for things to get even worse as winter approaches.

They say in one week, half of the country has reported a rise in COVID-19 cases. Dr. Chris Murray, with the Institute for Health Metrics and Evaluation, says that he is worried about winter as people are being less careful with cases down in some states, people will be inside together more often and the fact that flu season is coming up.

Experts are encouraging people to double down on COVID-19 prevention measures, like wearing a mask, social distancing and washing your hands.

A recent projection showed that if 95% of Americans wore a mask in public, about 100,000 lives could be saved by Jan. 1.

Experts say face masks are still the most powerful tool against the virus until there's a vaccine.