Preterm infants have suboptimal response to PCV7 vaccine

Preterm infants have a reduced response to some serotypes in the 7-valent pneumococcal conjugate vaccine (PCV7) compared with full-term infants, report researchers from the United Kingdom.

Their study found that in addition to a poor response to serotype 6B, preterm infants had a diminished response to serotype 23F, and several infants remained unprotected to at least 1 serotype after a booster dose of the vaccine.

Researchers examined response to the PCV7 vaccine among 133 preterm and 54 full-term infants who were immunized at 2, 3, and 4 months.

Although antibody titers increased after the 3-dose immunization series for preterm and full-term infants, preterm delivery was associated with a significantly lower (P<.01) antibody response to serotype 23F.

Geometric mean concentrations (GMCs) increased for all 7 vaccine serotypes after immunization of both preterm and full-term infants. Protective levels, however, defined as GMCs of 0.35 µg/mL or greater, against all 7 serotypes were achieved in only 36% of the full-term infants and 34% of the preterm infants.

Protective antibody levels to 6 of the 7 serotypes had declined by 12 months. The effect of preterm delivery resulted in significantly lower GMCs to serotypes 4,9V, 18C, 19F, and 23F, and preterm infants “were less likely to achieve putatively protective levels to serotype 23F only.”

At 12 months, only 22% of the full-term infants and 11% of the preterm infants had protective levels of antibodies against all 7 vaccine serotypes.

A booster dose increased protective levels in 28 of 29 full-term infants and 22 of 32 preterm infants. “Given that the majority of infants had an adequate response to a fourth dose, it is likely that the reduced response of our preterm cohort is due at least in part to immunological immaturity,” the researchers wrote.

An early booster dose for preterm infants who are unprotected is a practical solution, although examining responses to PCV7 would be costly, they note. Alternatively, household contacts could be immunized against pneumococcus.

The authors note that the lower responses of full-term infants in this study compared to previous studies and variation in the timing of the immunizations could have masked greater differences between the term and preterm cohorts.

Moss SJ, Fenton AC, Toomey JA, Grainger AJ, Smith J, Gennery AR. Responses to a conjugate pneumococcal vaccine in preterm infants immunized at 2, 3, and 4 months of age. Clin Vaccine Immunol. 2010;17(11):1810-1816.