Incidence of Invasive Pneumococcal Disease Declining Due to Vaccine

Emma Hitt, PhD

March 18, 2008

March 18, 2008 (Atlanta) — Incidence of invasive pneumococcal disease (IPD) has declined across all age groups, although rates of IPD caused by nonvaccine strains, while still low overall, have increased modestly, according to findings from the Centers for Disease Control and Prevention (CDC), Atlanta, Georgia, presented here today at the 2008 International Conference on Emerging Infectious Diseases.

The 7-valent pneumococcal conjugate vaccine (PCV7; Prevnar, Wyeth) was introduced in the United States in 2000 for children younger than 5 years.

Lead author Matthew Moore, MD, MPH, from the CDC, and colleagues identified cases of IPD at 8 surveillance sites during 2006 and compared the incidence to those detected during 1998 to 1999, before the vaccine was introduced.

The greatest decline in IPD — 78% — occurred in children younger than 5 years, but declines ranging from 14% to 42% were also observed in other age groups. For IPD caused only by serotypes included in the vaccine, the declines were even greater — a 99% drop in incidence of IPD was observed among children younger than 5 years.

Incidence of IPD caused by non-PCV7 serotypes increased slightly from 8.9 to 12.5, with the main increase being in serotype 19A, which increased from 0.8 to 2.8 cases per 100,000 people overall, representing approximately a 2.5-fold increase.

As of 2006, only 3% of all IPD cases were caused by serotypes included in PCV7 vaccine, whereas 67% and 69% were caused by serotypes included in a developmental 13-valent conjugate vaccine and the 23-valent polysaccharide vaccine (Pneumovax 23, Merck), respectively, the researchers noted.

PCV7, unlike the 23-valent polysaccharide vaccine, is effective in infants and toddlers because it is able to produce immunologic memory in children younger than 2 years. PCV7 is indicated for use in children younger than 5 years only (but not adults), whereas the 23-valent vaccine should not be used in children younger than 2 years.

"The developmental 13-valent vaccine, which includes 19A, manufactured by Wyeth, is in phase 3 clinical trials in children," Dr. Moore told Medscape Infectious Diseases. "If 19A were the only serotype included in that vaccine, it might not be as useful, but it includes 12 other serotypes, including the 7 in the existing vaccine," he said.

"The PCV7 vaccine is continuing to provide a substantial public health impact 6 years after its introduction," noted Dr. Moore. The CDC estimates that between 2001 and 2006, 170,000 cases of IPD and 9800 deaths were prevented as a result of the vaccine.

"These findings are very reassuring with respect to the efficacy of PCV7," noted Stephen I. Pelton, MD, chief of the Section of Pediatric Infectious Diseases, Boston Medical Center, Massachusetts. "However, we must assume that some risk groups should still be followed over time, and we do not know whether the rate of nonvaccine serotypes will increase," he told Medscape Infectious Diseases.

Dr. Pelton pointed out that the 19A strain appears to be causing significant disease in both children and adults. "There is a clone of 19A that is resistant to all oral antibiotics. If IPD from this strain is identified, initial treatment needs to include intravenous vancomycin, linezolid, or the fluoroquinolones (levofloxacin [is] licensed only for people...18 years [or older])," he noted.

The study was funded by the CDC's Emerging Infections Program. The authors and commentator have disclosed no relevant financial relationships.

International Conference on Emerging Infectious Diseases 2008: Slide Session J1. Presented March 18, 2008.


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