Preterm infants responded less robustly to the 13-valent pneumococcal conjugate vaccine following the three-shot infant series compared with term infants, but they caught up following the 12-month booster dose, a recent study found.
“Although the immune response to PCV13 1 month after the infant series was lower in preterm infants versus term infants, it is likely to provide adequate protection against disease,” reported Dr. Federico Martinón-Torres of Hospital Clinico Universitario de Santiago de Compostela and the Healthcare Research Institute of Santiago in Spain. Preterm infants, especially those born before 32 weeks, are at higher risk for invasive pneumococcal disease. “These results reinforce the importance of timely pneumococcal vaccination for all infants, including those born prematurely,” wrote Dr. Martinón-Torres and his associates (Pediatrics 2015 March 16 [doi: 10.1542/peds.2014-2941]).
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The researchers enrolled 100 healthy term and 100 healthy preterm infants, aged 42-98 days, in a parallel-group study in which the children received the standard PCV13 series at ages 2, 3, and 4 months, followed by the booster dose at 12 months. The children also received all other childhood recommended vaccines (DTaP, hepatitis B vaccine, inactivated poliovirus vaccine, Haemophilus influenzae type b vaccine, and meningococcal group C conjugate vaccine).
The World Health Organization’s established protection threshold for PCV13 response is an IgG concentration of 0.35 mcg/mL or greater. One month after the third dose, at least 85% of the infants achieved this IgG threshold, but a smaller proportion of preterm infants than term infants reached this threshold for serotypes 5, 6A, and 6B. Response for serotypes 6A and 6B generally decreased along with gestational age. Overall titers were generally higher for infants born between 32 and 37 weeks’ gestation compared with those born before 32 weeks’ gestation.
One month after the toddler dose, however, more than 97% of term and preterm infants achieved at least 0.35 mcg/mL of IgG antibodies for all serotypes except serotype 3, for which response was lower with younger gestational age. “Differences in IgG response between preterm and term infants almost disappeared after toddler vaccination, emphasizing the importance of timely administration of the booster dose,” the authors wrote.
Local reactions were similar across both infant groups and decreased with each subsequent dose. Decreased appetite, irritability, or decreased sleep occurred slightly more often among preterm infants than among term infants. Most reactions were mild or moderate, with fewer than 10% overall experiencing a severe reaction and only one (term) infant experiencing a fever above 40ºC following the toddler dose. One preterm infant also experienced a vaccine-related rash. Overall, 14% preterm infant and 5% of term infants experienced serious adverse events, primarily infections, not necessarily vaccine-related.
The study was funded by Pfizer. Dr. Martinón-Torres and several other investigators reported ties to GlaxoSmithKline, Sanofi Pasteur MSD, Sanofi Pasteur, Pfizer/Wyeth, Novartis, MedImmune, and/or Baxter. The remaining investigators, except for Dr. Concheiro-Guisán who reported no disclosures, are Pfizer employees and stockholders.