Arizona’s Flu Cases are at the Highest Level in 15 Years

If it seems like everyone you know is sick right now, it's not your imagination. According to the Centers for Disease Control (CDC), respiratory illnesses are rapidly spreading across the country at one of the highest levels in recent memory.

Right now, cases of respiratory syncytial virus (RSV), influenza (flu), and COVID-19 are at high levels and continuing to increase.

Influenza cases are of the most concern this year. Arizona is facing one of its toughest flu seasons in decades, and early data suggests it may be at its highest levels in 15 years. According to experts, several factors are stacking the deck this year.

Why is Arizona Experiencing the Worst Flu Season in Decades?

Arizona is in the middle of a severe flu wave. There have been more than 30,000 confirmed cases reported since October, according to the Arizona Department of Health Services. Nationally, the CDC reports the highest rate of doctor visits for flu‑like symptoms in 15 years.

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In Arizona, cases of the flu are hitting adults under 50 especially hard. This is different from the typical pattern. Typically, children and older adults tend to experience the most cases of the flu. The CDC classifies the 2024–25 season as “high severity,” the first time that label has been used in seven years.

Related: COVID-19’s Comeback in Arizona: What You Need to Know

Here's Why the Flu is Worse this Year

Two major factors are driving the surge of flu cases this year.

• A highly contagious Influenza A strain (H3N2 subclade K) is circulating widely across the U.S., causing more intense symptoms and spreading faster than usual.
• Post‑holiday travel and gatherings accelerated transmission, pushing case numbers sharply upward in December and January. This is always a factor following the holiday season.
• This season's flu vaccine was poorly matched to the strain of influenza currently circulating, leading to a 27% higher risk of infection.

More Reasons the Flu is Worse this Year

According to the Cleveland Clinic, influenza is unpredictable. It can become severe even in healthy adults, especially when an aggressive strain is circulating, as is the case this year.

This year’s flu vaccine is less effective because the dominant H3N2 strain evolved after the vaccine formula was finalized, meaning the shot doesn’t match the circulating virus as closely as usual, as reported by JAMA, the Journal of the American Medical Association.

READ: New CDC Guidelines for Covid Isolation Could Affect Arizona

While the CDC says flu vaccines typically reduce doctor and ER visits by 40–60% in a normal year, this year's inoculation offers much less protection against the fast‑moving strain.

Experts say vaccination remains the best defense against severe illness and hospitalization, but preventive measures like handwashing, rest, and staying hydrated can help slow the spread of this virus.