Infants who received heptavalent pneumococcal conjugate vaccination (PCV-7) at 2, 4, and 11 months were more likely than unvaccinated controls to have nasopharyngeal (in the nasal passages and upper part of the throat behind the nose) acquisition of pneumococcal serotype 19A, a leading cause of respiratory pneumococcal disease, according to a study in the September 8 issue of JAMA.
"A rapid increase in the presence of pneumococcal serotype 19A strains that are often multiresistant to antibiotics has been observed over the last decade. In the United States, serotype 19A is now the leading causative pneumococcal serotype of invasive and respiratory pneumococcal disease and the most frequently observed serotype in nasopharyngeal carriage. In the United States and other countries, the increase in serotype 19A disease was associated in time with the widespread implementation of PCV-7 in routine infant immunization programs," according to background information in the article. "Because spontaneous fluctuations in time and antibiotic selective pressure may have induced this serotype 19A increase, controlled studies are needed to assess the role of PCV-7."
Elske J. M. van Gils, M.D., of University Medical Center Utrecht, the Netherlands, and colleagues examined the association between PCV-7 vaccination and nasopharyngeal acquisition of serotype 19A pneumococci in 1,003 healthy newborns, with follow-up to the age of 24 months in the Netherlands, which has low antibiotic resistance rates. The study was conducted before widespread PCV-7 implementation in infants, between July 2005 and February 2008. Nasopharyngeal swabs were obtained at the age of 6 weeks and at 6, 12, 18, and 24 months. Infants were randomly assigned to receive 2 doses of PCV-7 at 2 and 4 months; 2 + 1 doses of PCV-7 at 2, 4, and 11 months; or no dosage (unvaccinated control group).