Reduced-dose pneumococcal vaccine schedule still offers protective benefits

Children who received either two primary doses of pneumococcal conjugate vaccine seven-valent or two doses and a booster instead of the currently recommended four-dose schedule had low rates of vaccine serotype carriage at two-year follow up.

“This study supports future implementation of reduced-dose pneumococcal conjugate vaccine seven-valent [PCV7, Prevnar, Wyeth] schedules,” Elske J.M. van Gils, MD, of the University Medical Center Utrecht, and colleagues wrote.

The current PCV7 vaccine schedule consists of three primary doses administered before age 6 months followed by a booster vaccine in the second year of life.

The researchers enrolled 1,003 healthy infants from a community in the Netherlands and randomly assigned them to either two doses of PCV7 at ages 2 and 4 months; two doses of PCV7 at ages 2 and 4 months followed by a booster dose at 11 months or a control group who remained unvaccinated.

Serotype carriage rates among both vaccine groups were significantly lower at 12-month follow up compared with the control group: 25% in the two-dose group, 20% in the three-dose group and 38% among those who had not been vaccinated.

Disparities between the vaccinated and unvaccinated groups continued to widen as more time passed:

Serotype carriage at 18-month follow up — 24% in the two-dose group and 16% in the three-dose group.
Serotype carriage at two-year follow up — 15% in the two-dose group, 14% in the three-dose group and 36% in the unvaccinated group.

Fewer doses could result in a more cost-effective schedule, could reduce the number of vaccines in already crowded childhood vaccine schedules and may be especially beneficial for developing countries that have difficulty delivering the complete four-dose schedule, according to the researchers.

Sanders EAM. JAMA. 2009;302:159-167.

The results of this study add to the reports from Quebec and the United Kingdom that demonstrate decline in invasive pneumococcal disease in children aged younger than 2 years receiving an abbreviated regimen (two doses plus one booster) of PCV7. The study suggests that herd effect as a result of decreased carriage of vaccine serotypes and therefore decreased transmission of vaccine serotypes from children younger than 2 years to unvaccinated individuals in the community can be achieved with a reduced-dose regimen.

It does not address whether some vaccine-preventable cases of invasive pneumococcal disease occur, at least in the first few years, in communities that opt for a reduced-dosing regimen compared with the three-dose plus one booster regimen.

Steven I. Pelton, MD

Boston Medical Center