In the United States, influenza, or the flu, is most common in January or February, but seasonal flu activity can begin as early as October, according to the Centers for Disease Control and Prevention (CDC).

The Colorado Department of Public Health and Environment began surveillance for the 2013-14 flu season Sept. 29 and will continue until May 24. A flu report is published weekly with a summary of activity in Colorado.

Dr. Rachel Herlily, deputy director of the department’s Disease Control and Environmental Epidemiology Division, said in a prepared statement, “Since flu season is so unpredictable, we recommend getting vaccinated as early as you can. It’s important to get vaccinated before outbreaks occur in your area, especially since it takes two weeks for the flu vaccine to become effective.”

For the week ending Oct. 26, no influenza activity was identified in the state. During this week, activity remained low in the United States as well. On average, Colorado sees about 750 hospital cases every year, but last year that number more than doubled, with 1,528 people hospitalized.

The CDC recommends a yearly flu vaccine for everyone 6 months of age and older, citing it as the most important step in protecting against the disease. The vaccine is designed to protect against three main flu strains that research indicates will cause the most illness during this year’s flu season.

Vaccine manufactures estimate 138 million to 145 million doses of influenza vaccine will be produced for the U.S. market this season, an increase from the initial estimate of 135 million to 139 million. About 30 million to 32 million of these doses will be quadrivalent flu vaccine and the rest will be trivalent.

Traditional flu vaccines — trivalent — are designed to protect against three strains of flu, while quadrivalent protect against four. As of Oct. 25, 113.9 million doses had been distributed.

Summit County doctor offices are also monitoring flu cases, and the three High Country Healthcare offices are offering walk-in clinic flu vaccine hours. Besides the traditional shot, there is also a nasal-spray flu vaccine. It takes approximately two weeks after vaccination to develop antibodies to protect against infection.

Vaccination is most important for people at increased risk for severe complications from the flu, including: children age 6 to 59 months, people who are more than 50, pregnant women, obese people, people with chronic conditions and more.

Flu symptoms usually come on faster than cold symptoms. Colds may take two or three days to develop, whereas flu symptoms can present themselves in just a few hours. Fevers are rare with colds; chills, muscle aches and headaches — more common with the flu — are not common with a cold.

A cold and flu tracker map on WebMD indicates that in Summit symptoms are moderate to severe, but HealthMap.org showed no cases in Colorado in the past week.

Flu vaccines are offered in many locations, including doctor’s offices, clinics, health departments, pharmacies and college health centers. Many employers and even some schools offer flu vaccines.

Visit http://flushot.healthmap.org to locate the closest flu vaccine provider.