HOUSTON — Flu season is underway.

Health department officials say the majority of flu-related hospital visits in Houston have been children four years old and younger.

Right now, 1.5 percent of all emergency room visits are due to flu-like symptoms, according to the Houston Health Department. That number usually peaks at 4 percent in January or February.

Before the number of flu cases increases, health officials answered some frequently asked questions about the flu.

How effective is this year’s vaccine?

The Houston Health Department expects this year’s vaccine to be a good match with the strains going around. However, even when it isn’t, they say the shot can still prevent millions of illnesses and deaths.

Can you get the flu more than once in a season?

Unfortunately, yes, because there are several strains of the flu. You can get infected with one strain of the virus, then come in contact with someone with another strain and get sick again.

How long is the flu contagious?

The CDC says people with the flu are contagious from one day before they show symptoms until up to seven days after. If a sick person coughs or sneezes, the virus can stay alive in the air for hours. The virus lives even longer on hard surfaces.

So all this is a good reminder to get your flu shot and wash your hands often.

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