Most parents have heard of strep throat, but one family of strep, Streptococcus pneumoniae, or pneumococcus, deserves special attention. Pneumococcal disease is the most common cause of vaccine-preventable death in the United States, killing more people than all other vaccine- preventable diseases combined. These bacteria present significant danger for both the youngest and oldest members of our families. Each year in the U.S., pneumococcus causes an estimated

• 7 million cases of ear infection in infants and young children;

• up to 570,000 cases of pneumonia, approximately one-fifth of which occur in infants and young children;

• 61,000 cases of bacteremia (that is, bacteria in the bloodstream that can lead to high fevers, pneumonia, or meningitis);

• 3,000 to 6,000 cases of meningitis; and

• more than 40,000 deaths.

In the 1880s, scientists first began to understand pneumococcus. In the 1940s, shortly after penicillin proved to be successful in treating certain bacterial infections, a study showed that a pneumococcal vaccine could prevent some infections in military recruits. By 1977, a vaccine was licensed that contained 14 different strains of pneumococcus, and in 1983 a 23-strain vaccine was licensed, but only for children older than 2 and for adults.

Unfortunately, children younger than 2 years bear much of the burden of pneumococcal disease. The incidence of invasive pneumococcal disease is 145 per 100,000 children under age 2; 54 per 100,000 adults older than 74; and 5 to 25 per 100,000 in the intervening ages.

A hundred years after pneumococcus was first isolated and shown to be a major cause of pneumonia, development began on a vaccine that could prevent pneumococcal disease in infants and young children. The vaccine was recommended by ACIP in October 1999 even before it was licensed by the FDA.