Duration of Infant Protection Against Influenza Illness Conferred by Maternal Immunization

Abstract

Influenza immunization of women during pregnancy protects the young infants against influenza illness. The duration of this protection remains unclear.OBJECTIVE To evaluate the duration of infant protection conferred by maternal immunization and its association with transplacental antibody transfer. DESIGN, SETTING, AND PARTICIPANTSInfants born to women who participated in a randomized, double-blind, placebo-controlled clinical trial in 2011 and 2012 on the safety, immunogenicity, and efficacy of trivalent inactivated influenza vaccine (IIV3) during pregnancy were followed up during the first 6 months of life for polymerase chain reaction (PCR)-confirmed influenza illness. In a secondary analysis of a subset of infants, hemagglutination inhibition (HAI) antibodies were measured. The study was performed at a single center in South Africa. The secondary analysis was performed in October 2014. EXPOSURE Maternal immunization for influenza.MAIN OUTCOMES AND MEASURES The vaccine's efficacy against PCR-confirmed influenza illness and the percentage of infants with HAI titers of 1:40 or more by age group. RESULTS There were 1026 infants (47.2% female) born to IIV3 recipients and 1023 infants (47.3% female) born to placebo recipients who were included in the analysis of the vaccine's efficacy. The vaccine's efficacy against PCR-confirmed influenza illness was highest among infants 8 weeks of age or younger at 85.6% (95% CI, 38.3%-98.4%) and decreased with increasing age to 25.5% (95% CI, −67.9% to 67.8%) among infants 8 to 16 weeks of age and to 30.3% (95% CI, −154.9% to 82.6%) among infants 16 to 24 weeks of age. Similarly, in the IIV3 group, the percentage of infants with HAI titers of 1:40 or more to the influenza vaccine strains decreased from more than 56% in the first week of life to less than 40% at 16 weeks of age and less than 10.0% at 24 weeks of age.CONCLUSIONS AND RELEVANCE Maternal immunization conferred protection against infection in the infants for a limited period during early life. The lack of protection beyond 8 weeks of age correlated with a decrease in maternally derived antibodies. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT01306669

Infant Protection Against Influenza Through Maternal Immunization

“…The study of Nunes at al 17 demonstrated a similar rapid decay in the first 2 months of life, 12,18 this study 17 provides more conclusive information indicating that there is limited efficacy of maternal influenza vaccination regarding infant protection beyond the second month of life. The investigators suggest that infant protection against influenza in the first few months of life is largely dependent on transplacentally transferred IgG antibodies, relative to breast milk-derived antibodies, as demonstrated by the lack of protection after concentrations of protective serum IgG antibodies have decreased significantly.…”

Experience and challenges on influenza and pertussis vaccination in pregnant women

“…31 A subsequent post-hoc analysis of the South African study reported that whilst vaccine efficacy was 86% (95% CI: 38–98%) in those <8 weeks of age, this declined to 25% (95% CI: -68-68%) and 29% (95% CI: -159-82%) in the 8–16 and 16–24 weeks age-groups, respectively. 32 Although not powered to address vaccine efficacy by narrower age-groups, the observed waning of immunity and efficacy in South Africa was corroborated in the Malian study where vaccine efficacy point estimate also declined from 69% when limited to analysing illness infants <2 months of age, to 33% when including all illness up to 6 months of age. 23 …”

The Impact of IgG Transplacental Transfer on Early Life Immunity

“…Moreover, maternal vaccination was associated with protection of infants from PCR-confirmed influenza illness. But, the protection was short-lived (first 8 weeks of life) and correlated with a decrease in maternally acquired antibodies (6). A longer period of infant protection (4 months) was observed following immunization of pregnant women from Mali during the third trimester of gestation (69).…”

“…Nevertheless, the incidence of other neonatal pathogens such as pertussis has increased over the last 3 decades (4). Importantly, even when infants passively acquire protective levels of pertussis-specific IgG, these antibodies rapidly wane during the first two months of life leaving the infant vulnerable to infection (5, 6). On the other hand, licensed maternal vaccines are not yet available against some life-threatening neonatal pathogens such as group B streptococcus or respiratory syncytial virus.…”