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Immunization Science

How effective is PCV7?

The article

Decrease of Invasive Pneumococcal Infections in Children Among 8 Children's Hospitals in the United States After the Introduction of the 7-Valent Pneumococcal Conjugate Vaccine. Kaplan, Sheldon L., Mason, Edward O, Jr, Wald, Ellen R., Schutze, Gordon E., Bradley, John S., Tan, Tina Q., Hoffman, Jill A., Givner, Laurence B., Yogev, Ram, Barson, William J. Pediatrics 2004;113: 443-449

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NNii's explanatory note: Serious bacterial sinus infections, pneumonia requiring hospitalization, and bacterial meningitis in children used to commonly cause serious 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 1987. 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 only infection with these 7 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 young infants and children.

The question

How protective is the 7-valent pneumococcal conjugate vaccine (PCV7) against pneumococcal infections?

The study

Investigators identified children with invasive infections caused by S pneumoniae at 8 children’s hospitals in the U.S. over a 9-year period (January 1, 1994 through December 31, 2002). They then compared the findings for the years 1994–2000 (before the vaccine was licensed) with the years 2001 and 2002, when the PCV7 was generally available to the population of children served by the 8 hospitals in the study.

The findings

The number of invasive cases of all pneumococcal infections cared for at the 8 children’s hospitals in the study declined in 2002 by 66% for children under 2 years of age, when compared with the years 1994–2000.

Also, researchers noted that the proportion of isolates resistant to penicillin decreased by almost 50% (the first time a decrease in antibiotic resistance has been noted since surveillance began in September 1993).

Two other serotypes (serogroups-15 and -33) which are not in the PCV7 vaccine have become an increasing proportion of the isolates from children with invasive disease.

The relevance/bottom line

PCV7 has been successful in preventing invasive pneumococcal disease in children and has resulted in the added benefit of a decrease in penicillin resistance among invasive pneumococcal isolates.

NNii’s comment

The number of invasive pneumococcal infections has decreased. However, it is not clear at this early stage of vaccine use whether other strains, such as types 15 and 33, may become increasingly more important over time. Questions that researchers are asking are whether future vaccines may need to protect against more pneumococcal serotypes.

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