Immunization Science

PCV7 and Antibiotic Resistance

The article

Reduction in High Rates of Antibiotic-Nonsusceptible Invasive Pneumococcal Disease in Tennessee after Introduction of the Pneumococcal Conjugate Vaccine. Talbot TR, Poehling KA, Hartert TV, Arbogast PG, Halasa NB, Mitchel E, Schaffner W, Craig AS, Edwards KM, and Griffin MR. Clinical Infectious Diseases 2004;39:641-648.

Explanatory note: Serious bacterial infections, such as pneumonia and bacterial meningitis in children, used to be common illnesses with potentially life threatening and damaging consequences. Many of these diseases have become uncommon since the Haemophilus influenzae, type b (Hib) conjugate vaccine was introduced in 1988. Many 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.

Some decades ago, all strains of Streptococcus pneumoniae were susceptible to the antibiotic penicillin. During the 1990s the frequency of antibiotic nonsusceptibility to penicillin and other antibiotics increased dramatically.

A vaccine against pneumococcal disease has been available for older people for many years. In 2000, a new conjugate vaccine, PCV7, became available for young children. The PCV7 vaccine contains the 7 most common pneumococcal serotypes causing invasive (serious) infections in children in North America, protecting against infection due to these 7 and some closely related serotypes. Prior to licensure there were concerns that nonvaccine serotypes of S. pneumoniae might simply replace the vaccine strains as the predominant strains causing invasive pneumococcal disease (IPD).

The question

What was the impact of PCV7 introduction on the epidemiology and antibiotic susceptibility of S. pneumoniae causing invasive pneumococcal disease (IPD) in Tennessee?

The study

In this study, researchers analyzed data from 5 urban counties in Tennessee—accounting for 40% of the state’s population—for cases of IPD occurring from 1995 to 2002.

The researchers compared the incidence of IPD in different age groups, the serotypes causing IPD, and the antibiotic susceptibility of the bacteria causing IPD before (1995-1999) and after (2000-2002) the introduction of PCV7.

The findings

The rates of IPD and the proportions of strains which were antibiotic nonsusceptible increased steadily in the years before the introduction of PCV7.

After PCV7 introduction, the annual rates of IPD decreased from more than 230 cases to 45.9 per 100,000 children younger than 2 years or age. Bacterial nonsusceptibility to penicillin in this age group declined from 59.8% in 1999 to 30.4% in 2002.

Rates of IPD and antibiotic nonsusceptibility also decreased in persons older than 2 years.

Rates of IPD due to vaccine serotypes declined after PCV7 introduction in all age groups. However, the rate of IPD due to serotypes not present in the vaccine increased as a cause of IPD in older children and adults.

The relevance/bottom line

PCV7 vaccination of young children has resulted in steady declines in the rates of invasive pneumococcal disease as well as the proportion of strains which are antibiotic nonsusceptible in children less than as well as in persons older than 2 years of age. However, an increase in the nonvaccine serotypes was also noted among isolates from persons older than 2 years.

NNii’s comment

This study, like other recent studies, has shown a dramatic decrease in IPD due to vaccine related serotypes of S. pneumoniae, both among infants and older individuals. In addition these studies have consistently shown a reduction of antibiotic nonsusceptibility.

Unlike other studies, these researchers demonstrated an increase in IPD due to nonvaccine serotypes. Unfortunately, more than a quarter of the isolates could not be obtained for testing. Further data on the serotypes that cause IPD will need to be collected over time.