A 2-plus-1 dosing schedule of the commonly used heptavalent pneumococcal conjugate vaccine showed satisfactory antibody responses to all serotypes of the bacteria, comparable with published immunogenicity studies on the 3-plus-1 dose schedule typically used.
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 obtained 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 symptom that was usually mild.
“At 13 months, 1 month after the third dose of PCV, 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,” the investigators said (Pediatr. Infect. Dis. J. 2005;24:108-14).
Serious adverse events observed for four children were lethargy/irritability, gastroenteritis, and scarlatina; one of these was considered as possibly related to the vaccinations. “All serious adverse symptoms disappeared within 3-6 days,” the authors wrote.
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,” the authors suggested that the use of fewer than four doses may be a practical option for the administration of the PCV.