Each year, 12,000 to 15,000 children under age 5 contract serious infections caused by the Haemophilus B influenzae bacterium, according to the federal Centers for Disease Control in Atlanta. Bacterial meningitis -- an inflammation of membranes around the brain and spinal cord -- strikes an average of 8,200 children in that age group, causing about 268 deaths annually. Also, there are thousands of non-meningitis cases resulting from Hib infection, ranging from pneumonia to epiglottitis -- a severe form of croup -- and bacteremia -- a bloodstream infection.

In addition to the costs of treating these preventable acute illnesses, there are substantial long-term expenses involved in caring for youngsters who recover but suffer developmental problems, such as deafness, learning disabilities and other neurological complications.

To protect infants and children from diseases that are most likely to occur in this age group, the American Academy of Pediatrics last month lowered the recommended age for receiving a Haemophilus influenzae type B vaccine to 2 months from 15 months.

The vaccine, which was approved by the Food and Drug Administration in October for use in children younger than 15 months, may be given in three doses, two months apart, and in combination with other vaccines, such as those for diphtheria-tetanus-pertussis and polio.

* Only one of three currently licensed Hib-conjugate vaccines is approved for use in children younger than 15 months at this time. (PICK UP CHART ON CHILDHOOD IMMUNIZATIONS ATTACHED.) SOURCE: Centers for Disease Control; American Academy of Pediatrics, October 1990