Flu Season Started Early in Parts of the U.S., and Experts Say You Should Consider Getting the Seasonal Jab ASAP. Here's What to Know

Every year, autumn brings gorgeous foliage, crisp air, shorter days—and a slew of respiratory illnesses. Flu season usually starts in October or November, but infection data suggests it has kicked off early in parts of the Northern Hemisphere. Flu rates began rising in August or September in many western states, including California, Washington, Alaska and Hawaii.

That’s unusual because the respiratory illness typically starts in the Southeast and spreads toward the West Coast. Infection rates have also been unusually early in places like Japan and the United Kingdom. We’re “looking at an early flu season this year,” said James Watt, deputy director of infectious diseases at the California Department of Public Health, at a briefing on October 6, reports Catherine Ho at the San Francisco Chronicle.

This early rise is concerning because people haven’t started getting their vaccines yet, says Danielle Zerr, an infectious-diseases specialist at Seattle Children’s, to Lena H. Sun at the Washington Post. The flu is caused by an infection with an influenza virus.

There are two subtypes of Influenza A—H3N2 and H1N1—and one type of Influenza B, according to the Centers for Disease Control and Prevention (CDC). The severity of each season depends on which version of the virus is spreading. H3N2 influenza strains are linked to more severe flu seasons and more hospitalizations.

This year, the other one, H1N1, is dominating. Flu spreads via droplets spewed when an infected person coughs, sneezes or talks. Symptoms generally appear one to four days after infection.

Signs of illness can include fever or feverish chills, cough, sore throat, runny nose, muscle aches and fatigue. A sick individual is most contagious during their first three days of symptoms. Since 2010, the flu has resulted in between 120,000 and 710,000 hospitalizations and has contributed to between 6,300 and 52,000 deaths each year in the U.S., according to estimates by the CDC.