A 2-plus-1 dosing schedule of the commonly used pneumococcal conjugate vaccine showed satisfactory antibody responses to all serotypes of the bacteria, comparable with published immunogenicity studies on the usual 3-plus-1 dose schedule.
The descriptive, nonrandomized trial was performed on children at 3, 5, and 12 months of age, and 99 of 101 healthy infants completed the study, wrote Helena Käyhty, Ph.D., of the National Public Health Institute, Helsinki, Finland, and her colleagues.
The investigators compared the geometric mean antibody concentrations for all serotypes with published immunogenicity results, including those from two efficacy trials—the Northern California Kaiser-Permanente study and the Finnish Otitis Media Vaccine Trial—that used the standard 3-plus-1 schedule with different end points—invasive disease or acute otitis media. A similar German trial with a 3-plus-1 schedule was also compared with the present study; it measured a slightly lower incidence of fever, a common, usually mild symptom.
“At 13 months, 1 month after the third dose of [PCV7], antibody concentrations measured in this study were as high as those in the previous Finnish, U.S., and German studies and were distributed similarly with respect to those in the previous Finnish study after four doses, indicating equally good immunologic priming after two to three doses in early infancy,” they said (Pediatr. Infect. Dis. J. 2005;24:108–14).
Serious adverse events in four children were lethargy/irritability, gastroenteritis, and scarlatina; one was considered as possibly related to the vaccinations. “All serious adverse symptoms disappeared within 3–6 days,” they wrote.
The PCV7, marketed under the trade name Prevnar, is part of the universal vaccination program for U.S. children in a 3-plus-1 schedule, but in other parts of the world, vaccination with PCV7 is still uncommon, according to Dr. Käyhty.
Due to the results of this study, and because “preliminary postmarketing surveillance reports from the United States suggest that two doses in the primary series are sufficient for protection, although additional information on the duration of protection is needed,” the authors suggested that the use of fewer than four doses may be a practical option for the administration of PCV7.