Dr. Ron Dagan and colleagues, from Soroka University Medical Center in Beer-Sheva, Israel, analyzed nasopharyngeal cultures from 262 children who had been given the pneumococcal vaccine or a control vaccine. All of the children were toddlers attending day care.

The pneumococcal serotypes included in the vaccine were 1, 4, 5, 9V, 14, 18C, 19F, 23F, and 6B. Most of the children were followed for more than 1.5 years after final vaccination. The researchers' findings are published in the April 1st issue of The Journal of Infectious Diseases.

The rate of VT pneumococci carriage was lower among children who received the pneumococcal vaccine than among those who received the control vaccine, the authors note. This difference was noted in all groups, but was most marked among children 36 months of age or younger.

Of the five vaccine serotypes that could be analyzed, the pneumococcal vaccine offered significant protection against 6B, 9V, 14, and 23F, but not against 19F, the researchers state.

Pneumococcal vaccination also appeared to offer protection against serotype 6A, a serotype not included in the vaccine. However, that was the exception, for most non-VT serotypes, carriage rates were higher in children who received the pneumococcal vaccine than those who received the control vaccine.

"We have demonstrated a marked protection against carriage of VT pneumococci in day care center attendees who received a 9-valent pneumococcal conjugate vaccine," the authors note. "Because day care centers are associated with extensive spread of pneumococci, our findings suggest that widespread vaccination may result in marked herd immunity."

Further follow-up is needed to determine the clinical significance of the increased rate of non-VT pneumococci carriage among the children who received the vaccine, the investigators note.

J Infect Dis 2002;185:927-936.