DEAR DR. DONOHUE: I have some questions about the flu and the flu vaccine. How do you tell flu from a cold? Does it give you diarrhea? Who needs to get a flu shot? Why do you have to get one every year? Does it always have to be gotten before the end of November? – B.D.

ANSWER: Flu – influenza – is a viral infection spread from person to person through fine droplets spewed into the air through a cough or sneeze. People who inhale those droplets come down with the flu one to four days later.

The illness begins abruptly. Body temperature rises, muscles hurt and the head aches. Infected people complain of a sore, scratchy throat and often have a dripping nose and a dry cough. They want to go to bed and not be bothered by anyone or anything. Colds do not have such dramatic symptoms.

Diarrhea is not a flu symptom. “Intestinal” flu is an unfortunate misnomer.

Provided there is a sufficient quantity of the vaccine, anyone who wants a shot can get it. People 50 and older and children between 6 months and 58 months are urged to get it. It protects 70 percent to 90 percent of vaccinees. It has to be given yearly because the virus changes yearly, and those changes have to be incorporated into the vaccine.

Flu season peaks in January. Vaccinated people begin to make antibodies about two weeks after getting the shot, but antibody production is not at its zenith until two months after the shot. That’s why October and November are the best times to get it, but you can get it anytime. It still provides some protection then, but not maximum protection at the peak of the season.

Flu is not a minor infection. It causes deaths, most of which occur in the older, the very young and those whose immunity is not up to par because of ill health. Those people would be foolish not to be immunized.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475.

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