Immunogenicity and safety of heptavalent conjugate vaccine against Streptococcus pneumoniae in pre-term Polish infants.

The purpose of the study was to assess post-vaccination immune response and occurrence of adverse events in the group of prematurely born infants. The study included 40 pre-term infants. Each child was vaccined four times (2, 4, 6 and 16 months) with the heptavalent conjugated pneumococcal vaccine (PCV7). Assessing of the level of antibodies was performed before vaccination, 4 weeks after primary series, before and 4 weeks after the booster dose. The research participants were qualified into 2 groups: group I - 19 children born before 30th gestational week, group II - 21 children born between the 30th and 34th gestational week. After the basic vaccination, an increase in the average antibody concentration in the area of all serotypes in most of the children tested was registered, with no significant differences observed between the groups. However, differences between individual serotypes were observed. The lowest values were found for serotype 6B. Before administering the booster dose, a significant drop in antibody titre in all of the children tested was noted. The last vaccination caused another significant increase in antibody concentration in both groups and the results obtained were markedly higher than those obtained after administering three vaccine doses. The majority of the children tested (with the exception of three from group II) achieved the preventive antibody level ≥ 0.35 μg/ml. In all of the children, no serious adverse events were observed. Our research showed, that heptavalent pneumococcal conjugate vaccine is immunogenic in children born before the completion of the 34th week of pregnancy. A booster dose of vaccine must be given at the right time to optimal response to the vaccine for all serotypes. Finally, any serious adverse events were observed.