Maternal immunization with pneumococcal 9-valent conjugate vaccine and early infant otitis media.

A randomized trial of an investigational 9-valent pneumococcal conjugate vaccine (PCV-9) or placebo given to pregnant women during the last trimester to prevent early infant otitis media (OM) was conducted. All infants received Prevnar(®) at 2, 4, 6, and 12 months. Clinic and adverse event records were reviewed to identify OM. Variables significantly related to acute OM by age 6 months (p<0.05) were: vaccine group (9 valent or placebo), sibling history of tympanostomy tubes, upper respiratory infection, and number of clinic visits by 6 months. Infant OM rates were similar between 6 and 12 months (58% and 56%). Results suggested that immunizing pregnant women with PCV-9 increased infants' risk of acute OM in the first 6 months of life, and this correlated with decreased infant antibody responses to their infant Streptococcus pneumoniae vaccine serotypes, but did not influence antibody responses to 3 other serotypes two of which were in maternal vaccine (types 1 and 5) and one was a control (type 7F). Explanations for these results include dampening of infant antibody production by high levels of passively acquired maternal pneumococcal antibodies and/or altered B lymphocyte immune responses in infants exposed to these specific polysaccharide antigens in utero.