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PCV serotypes nearly replaced by non-vaccine serotypes in Canada
After the introduction of conjugate vaccines, the overall colonization by pneumococcus has declined in recent years; however, non-vaccine serotypes have nearly replaced vaccine serotypes, according to recent study findings published in The Pediatric Infectious Disease Journal.
James D. Kellner, MD, of Alberta Children’s Hospital in Calgary, Canada, and colleagues conducted 10-point prevalence surveys of pneumococcal nasopharyngeal colonization in 6,149 healthy children aged 12 and 18 months and 4.5 years. They surveyed parents biannually from 2003 to 2005 and annually in 2006, 2010, 2011 and 2012 to determine serotype-specific trends in pneumococcal nasopharyngeal colonization after receipt of the 7-valent pneumococcal conjugate vaccine (Prevnar 7, Pfizer) and the 13-valent pneumococcal conjugate vaccine (Prevnar 13, Pfizer).
Overall, 17.7% of all patients were colonized with pneumococcus in 10 surveys. Pneumococcal colonization decreased from 19.9% in 2003-2006 to 13.3% in 2010-2012 (P<.001).
Ninety-nine percent of isolates were viable for serotyping. Fifty-six percent were non-vaccine serotypes, followed by 31% PCV7 and 13% PCV13. Before implementation of PCV13 in 2010, 10% of isolates were PCV7 serotypes and 31% were PCV13. However, 94% of isolated were non-vaccine serotypes in 2012.
Odds of colonization by a vaccine serotype were significantly decreased by two or more doses of either vaccine. Decreased odds of colonization with a vaccine type also were more decreased in the 4- to 6-year-old age group.
“In summary, in the late post-PCV7 and early post-PCV13 era, there has been a significant decrease in pneumococcal nasopharyngeal colonization in Calgary and a dramatic shift in the serotypes colonizing children,” the researchers wrote. “It will be important to determine if pneumococcal colonization will remain reduced in the long term, or ongoing serotype replacement will increase colonization rates back to pre-PCV7 levels.”
Disclosure: Three researchers report financial ties with Pfizer Canada and the Alberta Children’s Hospital Research Institute.
Perspective
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Streptococcus pneumoniae remains a leading cause of morbidity and mortality worldwide. Efforts to maintain high PCV coverage must continue because vaccines only work if children receive them. In the United States, in 2012, the coverage among 19- to 35-month-olds was 92.8% for three or more doses and 82.5% for four or more doses. The latest universal immunization schedule also includes a detailed footnote with recommendations for PCV13 and pneumococcal polysaccharide vaccine use in children and adolescents at increased risk based on their age and degree of risk. In countries with fewer resources and less reliable follow-up, a reduced PCV dose schedule could ensure broader vaccine coverage for the pediatric population and should be more cost effective.