A pneumococcal conjugate vaccine introduced in the U.S. 10 years ago appears to reduce pneumonia and serious associated complications, such as blood infections, in the vaccine's target range, children less than a year old, according to new research.
However, pneumonia and associated complications, including a lung infection called empyema, increased in older children, the study found. The results also show a narrowing of racial disparities in the rates of pneumonia and associated severe complications.
The study by researchers at The Children's Hospital of Philadelphia is called "National Hospitalization Trends for Pediatric Pneumonia and Associated Complications." It appears today in the online version of the journal Pediatrics. The study looked at 619,102 patients younger than 18 years old who were hospitalized for "community-acquired pneumonia" in the years 1997, 2000, 2003 or 2006 and recorded in the national Kids' Inpatient Database.
"The rate of hospitalizations for pneumonia declined among infants less than one year of age. This is the primary target population for pneumococcal vaccination, suggesting that the vaccine may contribute to reductions in infant pneumonia," said Samir Shah, M.D., M.S.C.E, senior author of the study and a pediatric infectious diseases physician at the Children's Hospital of Philadelphia. "While we aren't sure why we are seeing higher rates of pneumonia hospitalizations in older children, we think the decrease in infection rates in younger children is due to the vaccine."
The vaccine, known as PCV7, is administered to infants to prevent infection with the Streptococcus pneumoniae bacteria, the leading bacterial cause of pneumonia. Streptococcus pneumoniae, or pneumococcus, also causes ear infections, sinusitis, blood infections, and meningitis. There are more than 90 types of pneumococcal bacteria and PCV7 protects against seven of the most common strains. A recently licensed pneumococcal vaccine now protects against the 13 most common strains.
Before routine use of pneumococcal conjugate vaccine, infections caused more than 700 cases of meningitis, 13,000 blood infections and about 5 million ear infections each year in the U.S. The infection also contributed to about 200 deaths each year, according to the Centers for Disease Control and Prevention. After PCV7 was licensed, the rate of invasive pneumococcal disease such as meningitis and blood infections decreased by 76 percent among children 5 years and younger, according to the CDC.
"The impact of PCV7 on pneumonia has been more difficult to evaluate," said Dr. Shah, "because of the specific cause of pneumonia is sometimes difficult to determine."
The rate of hospitalizations for community-acquired pneumonia in the first year of life declined by 22 percent from 1997 to 2006, according to the study. Conversely, the rate of hospitalizations for pneumonia in children six to 12 increased 22 percent, and for children over 13 the rate increased by more than 40 percent. Lung complications related to pneumonia, such as empyema, were highest in children ages one to five years, the study found.
"This is the first national study to comprehensively examine rates of pneumonia-related complications before and after the introduction of the PCV7 vaccine," said Grace E. Lee, M.D., a lead researcher in the study and pediatric infectious diseases fellow at Children's Hospital. "Rates of systemic complications such as sepsis and respiratory failure decreased by 9 percent overall and approximately 35 percent for infants less than one year of age. The overall 9 percent decrease in systemic complication rates for the entire population in the study was largely attributable to the decrease in rates for infants and might be explained in part by the fact that infants have been the primary recipient of the vaccine."
"In contrast, rates of hospitalization for lung complications such as empyema increased by more than 70 percent for children between one and 18 years of age," said Dr. Lee. The reasons for such increases are not yet known.
The vaccine may also disproportionately benefit black children, shown in past studies to have a higher frequency of pneumococcal infections, including pneumonia. While rates of pneumonia were higher for black children compared to white children in all years of this study, the difference narrowed from a ratio of 1.98 in 1997 to a ratio of 1.59 in 2006.
Additional studies are needed to determine the underlying factors associated with these changes, the study authors noted.
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