The U.S. Centers for Disease Control and Prevention (CDC) has issued a health advisory that the number of flu cases has been rising among children and young adults in recent weeks, according to NBC News and Today.

Nationwide, flu cases are still low, but more than 90% are among children and young adults ages 5 to 24, according to the agency.

Experts found that most cases of flu are of the H3N2, a particularly troublesome strain, as it tends to mutate faster than other strains of influenza.

In the United States, H3N2 was the dominant strain during the 2017-18 flu season, when nearly 710,000 flu-related hospitalizations and 52,000 flu-related deaths occurred – the worst since the 2009 H1N1 flu pandemic.

Meanwhile, the CDC is investigating a flu outbreak at the University of Michigan where more than 525 students tested positive for the flu.

Officials expressed concerns and said college students and young people who are exposed to flu could spread the virus around the country as they often travel home for the holidays.

Infectious disease expert Dr. Isaac Bogoch of the University of Toronto said, “This is the time of the year when many people are going to be gathering together for the holidays for either Thanksgiving, Christmas or New Year’s, and there’s just the potential to amplify it.”

He urged people, especially those who are at risk for severe illness, should get vaccinated as the flu virus does not stay within a particular age group for long.

Dr. Bogoch said, “It’s coming. It’s not quite clear how large a flu season we’re going to have but we are going to have a flu season.”

In the United States, the flu season typically runs from October through May. The flu activity often tends to peak between December and February, according to the CDC.

Some infectious disease specialists have already said that the nation could be at risk for the severe flu season this year, urging people to get both flu and COVID-19 vaccines.

Experts are concerned that a surge in flu infections this winter could put an additional burden on the country’s health care system, which has already experienced a surge in COVID-19 cases.

The CDC’s health advisory recommends people with flu-like symptoms to get tested for both flu and COVID-19.