INTRODUCTION Pneumococcal infections are a major cause of mor­bidity and mortality and are associated with considerable economic burden on health systems. To prevent pneumococcal infections, 7-valent conjugate vaccines have been available for over a decade; more recently, 10- and 13-valent conjugate vaccines have been for­mulated, which are more immunogenic than vaccines with capsular polysaccharides only. In Cuba, a new vaccine candidate has been developed, PCV7-TT, a conjugate of tetanus toxoid with antigens of seven of the serotypes of Streptococcus pneumoniae with highest circu­lation in Cuba and in the world: 1, 5, 6B, 14, 18C, 19F and 23F.

OBJECTIVE Assess the safety of the vaccine candidate PCV7-TT in healthy adults and conduct a preliminary assessment of its immuno­genicity.

METHODS A phase I, double-blind clinical trial was performed at the National Toxicology Center in Havana, Cuba. Healthy male volunteers aged 18-35 years were randomly assigned to two groups: 20 received the vaccine candidate PCV7-TT and 20 the polyvalent antipneumo­coccal vaccine PNEUMO-23 used as control, each in a single intra­muscular dose. To assess safety, the occurrence of adverse events was monitored for 30 days following inoculation. To explore immuno­genicity, concentrations of serotype-specific antibodies was quantified before and 30 days after inoculation, as well titers of opsonophago­cytic antibodies. (National Clinical Trial Registry RPCEC00000133)

RESULTS Local adverse events were pain, redness, induration, increased sensitivity to touch, and warmth in the injection area. Pain was registered in 70% of individuals who received PCV7-TT and in 75% of those vaccinated with PNEUMO-23. Reported systemic adverse events were general malaise, headache and drowsiness. All adverse events appeared in the first 72 hours post inoculation and lasted no lon­ger than 3 days. One event was reported that was classified as severe in intensity and serious in consequences, but it was unrelated to vacci­nation appendicitis in one individual inoculated with the control vaccine. Before vaccination, all participants but one had antibody con­centrations ≥0.20 µg/ml against the vaccine strains; after vaccination 100% of individuals were positive and the concentrations of antibodies increased in previously positive volunteers. Some individuals had opso­nophagocytic antibodies against serotypes 1, 14, 19F and 23F before vaccination, with highest concentrations against serotypes 14 and 19F. After vaccination, the percent of individuals with opsonophagocytic titers ≥1:8 for all serotypes in the vaccine was >50% in both groups.

CONCLUSIONS A single dose of candidate vaccine PCV7-TT was safe when used in healthy adults. Preliminary results showed that it was able to activate an immune response against the serotypes of Streptococcus pneumoniae used.

KEYWORDS Invasive pneumococcal diseases, pneumococcal vac­cines, conjugate vaccines, immunization, randomized clinical trial, safety, Cuba