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Herd effect of PCV7 in children reduced pneumococcal carriage in Gambia
Roca A. PLoS Med. 2011;doi:10.1371/journal.pmed.1001107.
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Vaccinating young Gambian children with the 7-valent pneumococcal conjugate vaccine reduced vaccine-type pneumococcal nasopharyngeal carriage in nonvaccinated older children and adults, indicating a herd effect, according to new findings published in PLoS Medicine.
“Pneumococcal nasopharyngeal carriage is a proxy measure for pneumococcal disease,” Anna Roca, PhD, of the Medical Research Council Unit in Gambia, Africa, told Infectious Disease News. “If the vaccine has had an impact on reducing vaccine-type pneumococcal carriage, we expect that this effect will be translated into reducing pneumococcal disease in the study communities.”
For the cluster-randomized trial, Roca and colleagues investigated the effect of PCV7 (Prevnar, Wyeth) on pneumococcal nasopharyngeal carriage in 21 Gambian villages from December 2003 to June 2008.
Children aged younger than 30 months and those born during the trial in all study villages received PCV7. Older children and adults in 11 villages were randomly assigned to receive one dose of PCV7, and 10 villages were randomly assigned to the control meningococcal serogroup C conjugate vaccine.
The researchers collected nasopharyngeal swabs before vaccination (n=2,094), and 4 to 6 months (n=1,168), 12 months (n=1,210) and 22 months (n=446) after vaccination.
Before immunization, the overall prevalence of pneumococcal carriage in both groups was 71.1%, and after vaccination, the overall prevalence of pneumococcal carriage in all age groups decreased significantly, from 23.7% and 26.8% at baseline to 7.1% and 8.5% in vaccinated and control villages, respectively, according to the study.
Further, the researchers found that the prevalence of vaccine-type pneumococcal carriage was lower in vaccinated than in control villages among older children aged 5 to 15 years (OR=0.15; 95% CI, 0.04-0.57) and adults aged 15 years and older (OR=0.32; 95% CI, 0.10-0.98) at 12 months and among older children (OR=0.37; 95% CI 0.15-0.90) at 22 months. – by Ashley DeNyse
Disclosure: The study was funded by the U.K. Medical Research Council. Study vaccines were donated by Wyeth Lederle Vaccines (Pfizer) but played no role in the design of the study, writing or decision to publish this manuscript.
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