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. 2011 May;8(5):e1000441.
doi: 10.1371/journal.pmed.1000441. Epub 2011 May 31.

Maternal influenza immunization and reduced likelihood of prematurity and small for gestational age births: a retrospective cohort study

Saad B Omer  1 , David Goodman, Mark C Steinhoff, Roger Rochat, Keith P Klugman, Barbara J Stoll, Usha Ramakrishnan
Affiliations

Maternal influenza immunization and reduced likelihood of prematurity and small for gestational age births: a retrospective cohort study

Saad B Omer et al. PLoS Med. 2011 May.

Abstract

Background: Infections during pregnancy have the potential to adversely impact birth outcomes. We evaluated the association between receipt of inactivated influenza vaccine during pregnancy and prematurity and small for gestational age (SGA) births.

Methods and findings: We conducted a cohort analysis of surveillance data from the Georgia (United States) Pregnancy Risk Assessment Monitoring System. Among 4,326 live births between 1 June 2004 and 30 September 2006, maternal influenza vaccine information was available for 4,168 (96.3%). The primary intervention evaluated in this study was receipt of influenza vaccine during any trimester of pregnancy. The main outcome measures were prematurity (gestational age at birth <37 wk) and SGA (birth weight <10th percentile for gestational age). Infants who were born during the putative influenza season (1 October-31 May) and whose mothers were vaccinated against influenza during pregnancy were less likely to be premature compared to infants of unvaccinated mothers born in the same period (adjusted odds ratio [OR] = 0.60; 95% CI, 0.38-0.94). The magnitude of association between maternal influenza vaccine receipt and reduced likelihood of prematurity increased during the period of at least local influenza activity (adjusted OR = 0.44; 95% CI, 0.26-0.73) and was greatest during the widespread influenza activity period (adjusted OR = 0.28; 95% CI, 0.11-0.74). Compared with newborns of unvaccinated women, newborns of vaccinated mothers had 69% lower odds of being SGA (adjusted OR = 0.31; 95% CI, 0.13-0.75) during the period of widespread influenza activity. The adjusted and unadjusted ORs were not significant for the pre-influenza activity period.

Conclusions: This study demonstrates an association between immunization with the inactivated influenza vaccine during pregnancy and reduced likelihood of prematurity during local, regional, and widespread influenza activity periods. However, no associations were found for the pre-influenza activity period. Moreover, during the period of widespread influenza activity there was an association between maternal receipt of influenza vaccine and reduced likelihood of SGA birth.

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Conflict of interest statement

SBO was awarded the Maurice R. Hilleman Early-stage Career Investigator Award by the National Foundation for Infectious Diseases. The award is funded by an unrestricted educational grant to the National Foundation for Infectious Diseases from Merck and Co., Inc. However, SBO had no direct interaction with Merck related to this award. The other authors report no competing interests.

Figures

Figure 1
Figure 1. Influenza activity/analysis periods.
The numbers indicate births in each of the analysis periods.
See this image and copyright information in PMC

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