To the Editor: In their article on maternal influenza vaccination,Zaman et al. (Oct. 9 issue)1 address a very important preventivehealth intervention that had substantial benefits to both mothersand infants. However, the potential effect of breast-feedingon the outcome remains unclear. Was there an association betweenbreast-feeding and apparent immunity to respiratory illnessin the two study groups? Though the authors mention that themean numbers of weeks of exclusive breast-feeding were similarin the two groups, the range varied from 1 to 25 weeks. Wasany subgroup analysis done to investigate for an associationbetween the duration of breast-feeding and the development ofinfection? This is an important factor to consider, since previousstudies have shown that breast-feeding may decrease susceptibilityto influenza as a result of passive antibody transfer.2 It wouldbe interesting to note whether breast-feeding provided an additionalprotective factor to the infants in this study, as has beenobserved in epidemiologic data previously.3
Saira S. Tandon, M.D. Lutheran Medical Center Brooklyn, NY 11220 dr_saira_ahmad{at}hotmail.com
References
Zaman K, Roy E, Arifeen SE, et al. Effectiveness of maternal influenza immunization in mothers and infants. N Engl J Med 2008;359:1555-1564. [Free Full Text]
Ali HM, Scott R, Toms GL. The effect of foster feeding and bottle feeding expressed breast-milk on the susceptibility of guinea-pig infants to influenza virus. Br J Exp Pathol 1989;70:183-191. [Web of Science][Medline]
Chantry CJ, Howard CR, Auinger P. Full breastfeeding duration and associated decrease in respiratory tract infection in US children. Pediatrics 2006;117:425-432. [Free Full Text]
The authors reply: Although breast-feeding is known to havean effect on the infant immune response,1 its effect shouldbe equal in the two study groups in a randomized trial. In Table1 of our article, we report similar mean numbers of weeks ofexclusive breast-feeding in the two study groups (P=0.18).
We have now explored in detail the distribution of the durationof exclusive breast-feeding in each study group (Figure 1).Both groups showed a left-skewed distribution, with a peak aroundthe 20th week. However, the distribution in the influenza-vaccinegroup appears bimodal, with an additional peak around the fifthweek. The comparison of means and distribution does not suggestthat breast-feeding is a significant confounder. If anything,the slightly shorter duration of breast-feeding in the influenza-vaccinegroup would tend to reduce the observed effect of influenzaimmunization.
Figure 1. Distribution of the Mean Number of Weeks of Exclusive Breast-feeding.
The solid line represents the kernel-density estimation.
Effect modification by breast-feeding cannot be ruled out. Weplan to conduct a detailed secondary analysis to explore differentialvaccine effectiveness according to breast-feeding status ina variety of infant age groups and to assess the concentrationof IgA antibodies in breast milk.
Saad B. Omer, M.B., B.S., Ph.D. Emory University Atlanta, GA 30322
K. Zaman, M.B., B.S., Ph.D. International Centre for Diarrheal Disease Research Dhaka 1212, Bangladesh
Mark C. Steinhoff, M.D. Cincinnati Children's Hospital Cincinnati, OH 45229 m.steinhoff{at}gmail.com
References
Katona P, Katona-Apte J. The interaction between nutrition and infection. Clin Infect Dis 2008;46:1582-1588. [CrossRef][Web of Science][Medline]
Previous
