Though you wouldn’t know it with all the advertising in favor of the flu shot, the vaccine is really only moderately effective.

The reason for this poor showing — especially among older patients — is that the vaccine relies on the body’s ability to build antibodies.

The vaccine is actually a live, weakened form of the flu that triggers production of antibodies. But the ability to create antibodies diminishes as people age.

And although this weakened form of the virus is promoted as being safe, side effects can and do occur — including some that can be serious.

Another problem is that because of the way the flu shot is promoted, it can lead to a false sense of security, making people believe that they are better protected than they really are.

After getting a flu shot, many become lax about precautions that could keep them healthy during flu season.

Here are some steps to protect against flu:

• Eat a healthy diet. Eating a wide variety of fruits, vegetables, and whole grains will provide you with the necessary vitamins and minerals to maintain a robust immune system.

• Get at least eight hours of sleep each night. Sleep deprivation suppresses the immune system in much the same way that stress does, making it more likely that you’ll get sick.

• Wash your hands frequently with soap and water. Flu viruses spread mainly from person to person through droplets made when people with the flu cough, sneeze, or talk. The cashier who hands you change, the server who hands you a cup of coffee, or any of the other people you encounter in your daily life can spread the flu to you. You don’t even have to encounter the person with the virus; research shows it can live on surfaces such as doorknobs for hours.

• If you are sick, stay home and take care of yourself. Avoid contact with people who are sick as well.

• Take 2,000 mg of vitamin C a day.

• Avoid places where people live in close contact. College dormitories, military barracks, hospitals, and other such places are fertile breeding grounds for the virus.

If possible, avoid air travel and cruise ships during flu season. A Canadian study published in the Journal of Environmental Health Research reviewed passenger health histories after a five-hour flight between San Francisco and Denver, and found passengers were 113 times more likely to have caught a cold during the flight than during their normal daily lives.

If you must travel, take special precautions. Carry hand wipes to sanitize toilet seats and door handles and also keep a supply of zinc lozenges on hand. (Zinc was shown in clinical trials to shorten colds).

Use a saline nasal spray to keep nasal passages moist, as viruses can enter through dry membranes. Don’t use a decongestant spray because it can cause a rebound effect.