At least five children have died from the flu this fall, the Centers for Disease Control and Prevention said Friday, as cases related to the deadly viral strain increase across the U.S. with flu season underway.

Two children died in the second and third weeks of November, according to the CDC, which tracks influenza-related sicknesses and deaths weekly during the flu season. The agency did not say whether they had been vaccinated.

A high number of illnesses are being reported in Georgia and Louisiana, while Oklahoma and Utah are seeing a moderate level of sicknesses. Most of the U.S. is experiencing a mild season so far, with the most predominant strain being A(H1N1).

Federal health officials warn that illness ramps up during the holidays and during cold weather as more people spend time inside and in close quarters. Holiday parties and family get-togethers are also breeding grounds for disease.

The CDC recommends that everyone receive a flu vaccine, but especially children age 6 months and older, pregnant women, the elderly and people with compromised immune systems.

The 2017-2018 flu season was the deadliest in recent years, with 180 children dying from flu-related illness. In those cases, at least 80 percent of the fatal children weren’t vaccinated against flu. Health officials also recorded at least 79,000 deaths, 960,000 hospitalizations and 49 million illnesses.

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