Background: We assessed the safety and immunogenicity of 2 + 1 infant regimens initiated with the 13-valent pneumococcal conjugate vaccine (PCV13) and completed with the pneumococcal non-typeable Haemophilus influenzae protein D-conjugate vaccine (PHiD-CV). Methods: This partially blinded study randomized 6-12-week-old infants to receive two-dose priming and a booster (at ages 2, 4, 12-15 months) with: PCV13 at priming and PHiD-CV at boosting (PPS); PCV13 then PHiD-CV at priming and PHiD-CV at boosting (PSS); or PHiD-CV at priming and boosting (SSS control). All analyses were descriptive, i.e., no statistical significance tests were done. Results: The total vaccinated cohort at priming comprised 294 infants. Grade 3 adverse events were reported after 8.7% (PPS), 11.4% (PSS), and 16.9% (SSS) of primary doses (primary objective). No serious adverse events were considered vaccination-related. For most PHiD-CV serotypes, observed percentages of children reaching antibody concentrations ≥0.2 µg/mL and opsonophagocytic activity (OPA) titers above cutoffs were similar across groups 1 month post-priming and post-booster. Observed geometric mean antibody concentrations and OPA titers were lower for some PHiD-CV serotypes with the mixed regimens than with PHiD-CV only, especially for PSS. However, no tests of statistical significance were performed. Conclusions: Immunogenicity of the two mixed PCV13/PHiD-CV regimens seemed mostly similar to that of a PHiD-CV-only series, although observed antibody GMCs and OPA GMTs for some PHiD-CV serotypes were lower. No safety concerns were raised. The clinical relevance of the observed differences is unknown. Clinical trial registration: ClinicalTrials.gov: NCT01641133.
Keywords: Immunogenicity; PHiD-CV; infants; interchangeability; pneumococcal conjugate vaccine; safety.
Focus on the patientWhat is the context? Infant immunization programs worldwide include the pneumococcal conjugate vaccines Synflorix and Prevnar 13 to help combat pneumococcal diseases. Countries or regions choose whether to use Synflorix or Prevnar 13 and may decide to switch from one vaccine to the other. This can result in infants receiving a mixed vaccination regimen. Limited information is available about such mixed regimens. What is new? We assessed the immunogenicity of three infant vaccination regimens: 1) priming with two doses of Prevnar 13 and boosting with Synflorix; 2) priming with one dose of Prevnar 13 followed by one dose of Synflorix and boosting with Synflorix; 3) priming and boosting with Synflorix. The study showed that: Switching from Prevnar 13 to Synflorix at any time during the vaccination regimen did not seem to affect safety. When switching from Prevnar 13 to Synflorix at the time of boosting, immunogenicity was mostly similar to that of the Synflorix- only regimen. Switching vaccines during priming resulted in a trend toward lower immune responses for some vaccine components. What is the impact? This piece of evidence can be considered by doctors and health authorities when evaluating the possibility of switching pneumococcal vaccines in an immunization program or individual immunization regimen. Further effectiveness studies from countries or regions switching from Prevnar 13 to Synflorix (or vice versa) may shed more light on the feasibility of switching between these vaccines.