Flu season is officially here, off to its latest start in nearly 25 years

Health officials say the flu season is finally here - the slowest start in nearly 25 years.

Until this month, there weren’t enough flu cases in the U.S. to signal the start of the season. This is the latest start to a flu season since the winter of 1987-1988.

Flu season usually starts in December or January. Often, it’s half over by late February. CDC officials don’t know why this season was slow but it could be a combination of factors.

On Friday, CDC officials said one state - California - has had widespread cases for the last two weeks, and Missouri has seen a spike in reports of flu-like illness.

So far the flu vaccine seems well-matched to the strains making people sick. Last flu season was considered average.

What Is Flu Season?

Flu season is the time of year when the flu virus is most common. Flu season usually begins when cold weather appears. Why? There’s no apparent reason. It’s simply a characteristic of the flu and the timing of the seasons.

Outbreaks of the flu occur in different seasonal patterns around the world. In temperate climate zones, flu season will typically begin in the late fall and peak in mid-to-late winter. In tropical zones, flu seasons appear to be less pronounced, with year-round isolation of the virus.

Flu Season in the United States

Annual outbreaks of seasonal flu usually occur during the fall through early spring. In a typical year, approximately 5 to 20 percent of the population gets the seasonal flu. Flu-related deaths range from 3,300 to 48,600 (average 23,600). A seasonal flu vaccine is available.

The overall health impact of the flu varies from year to year. Unfortunately, rates of infection, hospitalizations, and deaths can’t be predicted, but by identifying flu symptoms, and knowing about flu treatment and flu prevention options, you can be better prepared to face the flu season.

How many shots does this year's vaccine require? Most people only need one. Children ages 6 months to 9 years, however, need two doses if they've never been vaccinated against flu, or if they only received one dose of the H1N1 vaccine last year. Those doses are given four weeks apart. The first dose primes the immune system, while the second provides immune protection, says Deborah Wexler, a family physician who founded the Immunization Action Coalition, an advocacy group that works to increase immunization rates. If a child needs two doses but only receives one, he or she will have little or no flu protection.

Is there a best time to get the flu shot?

There's no advantage to waiting, Bernstein says. The sooner you get it, the sooner you're protected.