According to results from a phase III safety and immunogenicity study presented, Prevenar 13 (Pneumococcal polysaccharide conjugate vaccine, [13-valent, adsorbed]) was shown to be immunogenic and generally well tolerated in healthy young children who had received at least three prior doses of Prevenar (Pneumococcal Saccharide Conjugated Vaccine, Adsorbed). These data were presented at the 7th International Symposium on Pneumococci and Pneumococcal Diseases (ISPPD) in Tel Aviv, Israel.

Prevenar 13 includes the seven serotypes (4, 6B, 9V, 14, 18C, 19F, and 23F) in Prevenar plus six additional serotypes (1, 3, 5, 6A, 7F, and 19A). Together, these 13 serotypes represent the most prevalent invasive disease-causing strains in young children worldwide.

"Prevenar has significantly reduced the incidence of invasive pneumococcal disease in young children in areas where it is routinely used. The data from this phase III study showed that children up to 5 years of age previously vaccinated with Prevenar had an increased immune response against all 13 serotypes included in Prevenar 13," says Robert W. Frenck, Jr., M.D., the study's coordinating investigator and professor of pediatrics, Cincinnati Children's Hospital Medical Center.

Also presented at this meeting were data comparing immunogenicity and functional antibody responses in young children who were administered Prevenar and Prevenar 13. It has been suggested that pneumococcal conjugate vaccines that include serotypes 6B and 19F may provide some cross protection against invasive disease caused by 6A and 19A. The data presented suggest that the immunogenicity and functional antibody responses induced by Prevenar 13 for serotypes 6A and 19A were greater than the responses elicited by Prevenar. These results are believed to be attributable to the inclusion of these two serotypes in Prevenar 13.

"These data further suggest the importance of providing direct coverage against the 13 most common pneumococcal disease-causing serotypes worldwide," says Emilio Emini, Ph.D., chief scientific officer, Vaccine Research, Pfizer Inc. "Notably, serotypes 6A and 19A, which are included in Prevenar 13, are prevalent in many regions of the world."

Abstract #153: Immunogenicity and Safety of 13-valent Pneumococcal Conjugate Vaccine in Children Previously Immunized with 7-valent Pneumococcal Conjugate Vaccine

This abstract pertained to an open-label Phase III study that was conducted to evaluate the immune response of 307 children between the ages of 15 months and 5 years who received at least three prior doses of Prevenar (the evaluable immunogenicity population). The study measured immunoglobulin G (IgG) and response was assessed as greater than or equal to 0.35 mcg/mL for each of the Prevenar 13 serotypes measured one month after the last scheduled vaccination (the study's primary endpoint).

The study showed that children aged >15 months to <2 years who received two doses of Prevenar 13 responded to vaccination with Prevenar 13 with a high proportion of responders to the six additional serotypes included in the vaccine, ranging from 94.5 percent (serotype 3) to 100 percent (serotypes 1, 7F and 19A, n=126). In children =2 to =5 years old who received one dose of Prevenar 13, response to vaccination was also high for the six additional vaccine serotypes with proportion of responders ranging from 92 percent (serotype 3) to 100 percent (serotype 19A, n=181). Children in both age groups also experienced a booster effect of increased immunity against the seven common serotypes in both vaccines.

In addition, data from the study showed that Prevenar 13 was generally well tolerated. The most commonly reported adverse reactions were injection-site reactions, fever, irritability, decreased appetite, and increased and/or decreased sleep. Most local reactions were mild and lasted approximately two days.

Abstract #572: Immunity to Serogroups 6 and 19 by CRM197-based PCV7 and PCV13: The Relative Importance of Direct and Cross Protection

This abstract described data from five Phase III pediatric clinical studies conducted in the United States and Europe that assessed and compared the immune responses to serotypes 6A and 19A for infants and toddlers vaccinated with Prevenar and Prevenar 13. Children in the studies received immunizations of either three infant doses followed by a toddler dose or two infant doses followed by a toddler dose, according to the National Vaccine Program in each country. Immune responses to serotypes 6A and 19A were analyzed by testing blood samples using ELISA anticapsular IgG (GMCs and percent responders achieving the World Health Organization-established threshold of greater than or equal to 0.35 mcg/mL) and functional opsonophagocytic assay (OPA) after vaccination with Prevenar or Prevenar 13.

The data showed concordance between IgG and OPA activity to serotype 6A with both Prevenar and Prevenar 13, but the functional antibody response induced by Prevenar 13 was four to 25 times greater than that for Prevenar.

Moreover, although Prevenar elicited IgG antibody responses to serotype 19A, it elicited only a negligible functional response. Prevenar 13 IgG responses were 1.3 to 2.5 times greater than Prevenar and Prevenar 13 showed a marked anti-type 19A functional OPA activity.