Pneumococcal vaccine associated with increase in penicillin-resistant bacteremia

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There is good news and bad news with the new heptavalent conjugate pneumococcal vaccine (PCV7). The vaccine is associated with a 57% decrease in the overall incidence of pneumococcal bacteremia, but the percentage of penicillin-resistant isolates has increased in the post-licensure period.

Researchers at The Children's Hospital of Philadelphia, Pennsylvania, led by Dr. Andrew P. Steenhoff, evaluated 188 episodes of pneumococcal bacteremia and 55 episodes caused by other respiratory pathogens -- as a type of control -- in children aged 18 and younger admitted to their institution between January 1999 and May 2005.

Causative organisms were Streptococcus pneumonia, Neisseria meningitidis, Hemophilus influenzae and Moraxella catarrhalis, the team reports in the April 1st Clinical Infectious Diseases. For cases of pneumococcal pathogens, serotype distribution and resistance were analyzed.

Incidence rates of pneumococcal bacteremia and bacteremia from other respiratory organisms were evaluated with reference to the introduction of PCV7, which was added to routine childhood immunizations in October 2000.

Between the periods 1999-2000 and 2004-2005, the incidence of S. pneumoniae bacteremia dropped 57%, from 7.51 to 3.25 cases per 10,0000 emergency room visits. The incidence of bacteremia caused by other respiratory pathogens did not change.

Vaccine serotypes accounted for 85% of cases of pneumococcal bacteremia in 1999. That rate fell to 34% of cases of bacteremia by 2005.

The percentage of isolates resistant to penicillin was 25% in 1999-2000, increasing to 39% by 2004-2005.

Rates of pneumococcal bacteremia caused by non-vaccine serotypes were not different between the two periods. However, the percentage of episodes caused by vaccine-related serotypes (ie, of the same serogroup but not the exact same serotype as in the vaccine) rose from 6% before licensure to 35% after.

This has the potential "to change the clinical epidemiology of pneumococcal disease," the investigators warn. "Continued surveillance of invasive pneumococcal serotypes is important to fully understand the impact of PCV7 and to define whether such changes merit alteration of the composition of the conjugate vaccine."

Clin Infect Dis 2006;42 907-914.