Medical experts are sounding the alarm on the potential for a fourth nationwide surge in COVID-19 cases as case numbers are on the rise again.

Two counties in the Hudson Valley are seeing a steep spike.

About one month ago to the day, Ulster County saw just over 1,500 active cases. About 30 days later, the county is breaking 1,900 positive cases.

Duchess County is in that same boat. The county government’s COVID-19 dashboard shows the month of February ending with just over 1,000 active cases. Right now, the county is dealing with more than 1,400 positive cases.

Doctors say new variants are to blame, but it’s not the only reason.

"What we're likely seeing is because of things like spring break and pulling back on the mitigation methods that you've seen now several states have done that," says Dr. Anthony Fauci, director of National Institute of Allergy and Infectious Diseases.

"A lot of the spread is happening among younger people, 10 to 19 and also 20 to 29, and that's the group that is moving around, kind of relaxing, getting infected," says Dr. Ashish Jha, dean at Brown University School of Public Health.

Experts are urging everyone to continue safety practices like mask-wearing and social distancing. They're also suggesting people hold off on travel until more people are vaccinated.