Published Online: February 10, 2012
Infections with Streptococcus pneumoniae (pneumococcus) are a major cause of child mortality, with an estimated one million deaths each year, occurring mostly in the developing world. Several types of pneumococcal vaccines are available, including the conjugate vaccines which are given primarily during infancy and the polysaccharide vaccines which are licensed for use in older children and adults. The 23-valent pneumococcal polysaccharide vaccine (Pneumovax®) provides wider serotype coverage than conjugate vaccines (which contain up to 13 serotypes) but is widely considered to be weakly immunogenic in children under 2 years old and therefore is not licensed for use in this population. However, this dogma is based on limited evidence derived from studies involving small sample sizes that examined responses to a limited number of serotypes.
In The Journal of Allergy and Clinical Immunology (JACI), Licciardi et al measured the functional immune response in 12-month old Fijian infants (n=55) following a single immunization with Pneumovax®. Previously, the authors reported that these 12-month old infants can generate robust serotype-specific IgG responses to the majority of vaccine serotypes. The investigators have now extended their findings to show that the humoral immune response to Pneumovax® in these infants is functionally active using the World Health Organization (WHO) gold-standard opsonophagocytosis assay (OPA) as well as the antibody avidity assay which measure the potency of the immune response to kill the pneumococcus.
71% of infants produced strong OPA responses against four of the eight serotypes tested while 30% produced high avidity serotype-specific IgG antibodies to 10 of 23 serotypes after two weeks following Pneumovax® immunization. Approximately 20% of all infants were still able to produce functional antibody responses using both methods by 5 months old. The authors also found that while protective functional responses were observed for most serotypes that cause disease in Western countries, responses to many of the epidemiologically-relevant serotypes for young children in developing countries were less prominent. In summary, these findings show for the first time that Pneumovax® immunization of infants at 12 months old induces highly-functional antibodies. Further studies evaluating the use of Pneumovax® in high-risk populations are warranted, although the poorer responses to disease causing serotypes may limit its usefulness in this setting.
The Journal of Allergy and Clinical Immunology (JACI) is the official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.