Immunization Science

Impact of a large PCV7 Vaccination Program

The article

Postlicensure Surveillance for Pneumococcal Invasive Disease After Use of Heptavalent Pneumococcal Conjugate Vaccine in Northern California Kaiser Permanente. Black S, Shinefield H, Baxter R, Austrian R, Bracken L, Hansen J, Lewis E, Fireman B. The Pediatric Infectious Disease Journal 2004;23(6):485-489.

Explanatory note: Serious bacterial sinus infections, pneumonia requiring hospitalization, and bacterial meningitis in children used to be common illnesses with potentially life threatening and damaging consequences in young infants and children. Many of these diseases have become uncommon since the Haemophilus influenzae, type b (Hib) conjugate vaccine was introduced in 1988. Much of the remaining diseases of these types are caused by Streptococcus pneumoniae, a similar but unrelated bacterium. Unlike with Hib where there was only one type, there are more than 90 types (or serotypes) of S pneumoniae.

The PCV7 vaccine contains the 7 most common pneumococcal serotypes causing invasive (serious) infections in children in North America. Thus, the PCV7 vaccine protects against infection only with these 7 and closely related serotypes. These 7 serotypes also are the most likely to be resistant to the antibiotics used to treat these infections. PCV7 was licensed in February 2000 in the United States for routine administration to children younger than 2 years of age; during this period of time, it has often been in limited supply. This study details results of a 3.5-year surveillance of pneumococcal infection after licensure of PCV7.

The question

What has been the effect of the vaccination program for young children against pneumococcal disease in the population of a large HMO?

The study

This study surveyed for invasive pneumococcal disease among approximately 3.1 million people enrolled in the Northern California Kaiser Permanente (NCKP) medical program.

Surveillance included laboratory tests for serotype and resistance, data from hospital admissions, and immunization records among other methods.

During the 3.5-year period, both children and adults in the NCKP population were under surveillance, to assess the direct and indirect effects of the vaccination program.

The study also evaluated the impact of the introduction of the vaccine on patterns of antibiotic resistance in pneumococci.

The findings

This study found that during the last year of observation, no cases of vaccine serotype disease were seen in children less than 1 year of age compared with 16 to 34 cases per year in the years before PCV7 was used. For all children less than 5 years of age, similar reductions were observed. There also was a significant reduction of infections due to vaccine-containing serotypes in adults, especially those 20-30 and 65 years of age and older.

The study also found that pneumococcal disease caused by serotypes not included in the vaccine did not increase.

Additionally, the surveillance showed that high-level resistance of pneumococci to the antibiotic penicillin fell from a peak of 15% in 2000 to 5% in the first half of 2003. Similar trends were seen for other antibiotics.

The relevance/bottom line

The conjugate pneumococcal vaccine reduced the burden of pneumococcal disease in children less than 5 years of age in the NCKP population. Antibiotic resistance in strains causing invasive disease decreased and there was no evidence of serotype replacement by non-vaccine strains.

NNii’s comment

This study and similar studies by CDC for the United States, have shown a dramatic decrease in invasive disease due to S pneumoniae, both among infants and older individuals, despite vaccine shortages that have necessitated compromises in the use of the vaccine. Unexpected benefits of the vaccine include a reduction of serious infections among adults and a decrease in antibiotic resistance.