Parents concerned about getting their babies and preschoolers vaccinated against the flu have new reassurance about the shot's safety: The largest population-based study of young children has found few problems, none of them serious.

The vaccine has a good safety record, but previous studies in children have been much smaller. This study, published in an October 2006 issue of the Journal of the American Medical Association, included 45,356 children ages 6 months to 23 months old. The researchers found only a slight increase in vomiting and diarrhea, but the cases were generally mild. They don't know whether the reaction was caused by the vaccine or another reason, such as exposure to gastrointestinal bugs in doctors' waiting rooms. Additional research is still needed in children ages 2 through 4 years old.

Young children need to be vaccinated because they have more flu-related complications, including pneumonia, than any other age group except adults over 65. The Centers for Disease Control and Prevention had previously recommended that children ages 6 months to 23 months be vaccinated, but in February 2006 it extended its recommendation to up to 59 months.

The CDC has said that even flu vaccines containing thimerosal, a mercury-based preservative, can safely be given to children because there is no convincing evidence of harm caused by the small amount of thimerosal in the shot. Our chief medical consultant agrees that those vaccines are worth taking, given the clear risk of complications from the flu vs. only the potential risks from thimerosal.

Reserves of the flu shot, which is often available for free, seem to be adequate for most children. But there may be a shortage among 3-year-olds because the sole supplier of vaccines approved for that age group booked its supply before the CDC issued its new recommendations. If you can't get your child vaccinated, make sure you and other members of your family get the shot to help prevent the spread of the disease to the child.

Caretakers of young children should also take these extra steps to prevent transmitting the infection:

• Cough or sneeze into tissues and dispose of them after using.
• Use disinfectant wipes on telephones and computers that others use.
• Wash hands frequently with soap.
• Avoid close contact with sick people.
• Shore up your immune system by eating well, exercising regularly, getting plenty of rest, and reducing stress.
• Quit smoking, since smokers and family members exposed to smoke are more likely to get respiratory infections.
• Don't rely on herbs or supplements. Researchers have tested many of these products, such as echinacea and ginseng, and, so far, none of them has proved effective at preventing flu.