Pneumococcal disease rates down significantly post-vaccine

Since the approval of a vaccine against pneumococcal bacteria for young children in 2000, rates of invasive pneumococcal disease (IPD) are down significantly in all age groups, while rates of IPD caused by non-vaccine strains are modestly on the rise. Researchers from the Centers for Disease Control and Prevention (CDC) report their results today (March 18) at the 2008 International Conference on Emerging Infectious Diseases in Atlanta, Georgia.

“This vaccine is continuing to provide a very substantial public health impact 6 years after its introduction. We estimate that between 2001 and 2006, 170,000 cases and 9,800 deaths were prevented as a result of this vaccine,” says Matthew Moore of the CDC, a lead researcher on the study.

Streptococcus pneumoniae, also called pneumococcus, is one of the most common causes of bacterial pneumonia and deadly bloodstream infections in the United States. It can also cause bacterial meningitis in children and adults. In its less severe forms it commonly causes ear infections. Pneumococcus bacteria can be found colonizing many people’s noses without causing infection. Why it suddenly invades the body and causes disease is unknown.

A vaccine against pneumococcal disease has been available for adults and children over 2 years of age since the 1980s, but in 2000 a new vaccine, known as PCV7, was approved by the FDA for children under 5 years of age.

The CDC has been tracking the incidence of IPD, the most severe form of the disease – defined as meningitis or a bloodstream infection, which can include some cases of pneumonia – since the introduction of the vaccine. Moore and his colleagues compared rates of IPD in 2006 with reported rates for 1998-1999, just before PCV7 was introduced.

The researchers found a significant decline in IPD rates for all age groups (-78%, under 5 years; -38%, 5-17 years; -39%, 18-49 years; -14%, 50-64 years; -32%, 65-79 years; and -42%, 80 years and older) with even greater declines in IPD caused by those strains included in the PCV7 vaccine. The incidence of IPD caused by strains not included in the vaccine rose by 40%. One of the non-vaccine strains, 19A showed an increase of 264%, but Moore cautions that because these strains were relatively uncommon before the introduction of the vaccine, the increase in actual numbers is still small.