SAN DIEGO – Children who receive just one of the recommended two doses of the 13-valent pneumococcal conjugate vaccine still derive indirect protection, new data suggest.
Colonization rates were similar for immune and nonimmune children, based on surveillance data for the first 2 years after the vaccine’s introduction. The findings come from a study at the Boston Medical Center of 4,338 children under age 60 months. Roughly one-third were considered nonimmune because they did not receive sufficient doses of the vaccine.
Dr. Stephen I. Pelton
Nasopharyngeal colonization with PCV13-unique serotypes fell in the overall population after the introduction of the vaccine. Importantly, colonization declined by at least 50% in the nonimmune group at about 1.5 years after the vaccine was introduced, when roughly 75% of eligible children had received it.
Although it took time for the nonimmune group to catch up with their immune peers, the vaccine reduced serotype-specific colonization in children regardless of their immune status, commented Dr. Stephen I. Pelton, a professor of pediatrics and epidemiology at Boston University. "No change in overall prevalence of pneumococcal colonization is observed," he said at IDWeek.
Introduction of the similar PCV7 vaccine was associated with a greater reduction of cases of pneumococcal disease in nonimmunized children than in their immunized counterparts (MBio. 2011;2:e00309-10). The researchers in that study attributed the shared benefits to the vaccine’s impact in reducing nasopharyngeal carriage and transmission of vaccine serotypes.
The records of children aged 59 months or younger who received care at the Boston Medical Center’s primary care center were reviewed to determine vaccination status. Children under age 12 months were considered immune if they received two doses of PCV13 vaccine, and older children were presumed immune if they received one dose.
Pneumococcal colonization was based on the serotypes of Streptococcus pneumoniae isolates obtained from nasopharyngeal swab samples. Colonization analyses used 25-week rolling intervals, for example, weeks 1-25, weeks 2-26, and so on.
Analyses showed good uptake of the vaccine in all age groups. The percentage of children considered immune rose steadily over the 2-year period and peaked at 80%, Dr. Pelton reported.
On average, 32% of children were considered nonimmune during the study period, but the proportion decreased over time.
The overall prevalence of colonization was essentially stable during the study period, but the prevalence of colonization specifically with PCV13-unique serotypes fell. A distinct seasonal pattern was also evident.
"By week 28, we could already see a difference between the unimmunized group and the immunized group," Dr. Pelton explained. "We saw a rapid increase in PCV13 carriage during the fall, projecting on into the winter season [in the former], whereas we have a blunting in the children who are immunized in terms of the acquisition of PCV13 serotypes."
An indirect effect of the vaccine – a reduction by at least 50% in colonization with PCV13-unique serotypes that persisted among nonimmune children during a comparable season – was achieved at week 81. At that point the prevalence stood at about 3 cases per 100 nonimmune children. This outcome occurred when vaccine uptake reached 75%.
Colonization among nonimmune children fell to the levels seen among immune children at week 52 after the PCV13 vaccine was introduced. By this time, vaccine uptake hit 65%.
The researcher also looked at the impact of a single dose of PCV13 vaccine among children 24-59 months of age during the first half-year after the vaccine’s introduction. Colonization with PCV13-unique serotypes rose during the fall and winter months among children who did not receive any vaccine doses, but the rise was blunted among those who received one dose of vaccine.
The blunting of colonization "strongly suggests to us that a single dose is adequate to prevent colonization with PCV13 serotypes, and we can say that because [the blunting] occurs very early, before we would expect, we were able to observe a significant indirect effect in the population," Dr. Pelton said.
IDWeek is the combined annual meetings of the Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, the HIV Medicine Association, and the Pediatric Infectious Diseases Society.
Dr. Pelton disclosed that he has received honoraria and research funding from Merck, GlaxoSmithKline, and Pfizer. The study was funded by the Thrasher Research Foundation and Pfizer.